From 46d7adefe08e5fde1400261278449dccd082d0f4 Mon Sep 17 00:00:00 2001
From: silverwind <me@silverwind.io>
Date: Wed, 3 Dec 2025 03:13:16 +0100
Subject: [PATCH] Enable TypeScript `strictNullChecks` (#35843)

A big step towards enabling strict mode in Typescript.

There was definitely a good share of potential bugs while refactoring
this. When in doubt, I opted to keep the potentially broken behaviour.
Notably, the `DOMEvent` type is gone, it was broken and we're better of
with type assertions on `e.target`.

---------

Signed-off-by: silverwind <me@silverwind.io>
Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
---
 eslint.config.ts                              |   2 +-
 tsconfig.json                                 |   2 +-
 web_src/js/bootstrap.ts                       |   2 +-
 web_src/js/components/ActivityHeatmap.vue     |   4 +-
 web_src/js/components/ContextPopup.vue        |   4 +-
 web_src/js/components/DashboardRepoList.vue   |   4 +-
 web_src/js/components/DiffCommitSelector.vue  |  10 +-
 web_src/js/components/DiffFileTree.vue        |  12 +-
 web_src/js/components/RepoActionView.vue      |   4 +-
 .../js/components/RepoActivityTopAuthors.vue  |   6 +-
 .../js/components/RepoBranchTagSelector.vue   |  45 +++---
 web_src/js/components/RepoContributors.vue    |  14 +-
 web_src/js/components/RepoFileSearch.vue      |  14 +-
 web_src/js/components/ViewFileTree.vue        |   6 +-
 web_src/js/components/ViewFileTreeItem.vue    |   2 +-
 web_src/js/components/ViewFileTreeStore.ts    |   7 +-
 web_src/js/features/admin/common.ts           |  38 ++---
 web_src/js/features/admin/config.ts           |   2 +-
 web_src/js/features/admin/selfcheck.ts        |   4 +-
 web_src/js/features/captcha.ts                |   4 +-
 web_src/js/features/citation.ts               |   6 +-
 web_src/js/features/clipboard.ts              |   7 +-
 web_src/js/features/colorpicker.ts            |  15 +-
 web_src/js/features/common-button.ts          |  18 +--
 web_src/js/features/common-fetch-action.ts    |   2 +-
 web_src/js/features/common-form.ts            |   8 +-
 web_src/js/features/common-issue-list.ts      |  11 +-
 web_src/js/features/common-organization.ts    |   2 +-
 web_src/js/features/common-page.ts            |   4 +-
 .../js/features/comp/ComboMarkdownEditor.ts   |  53 +++----
 web_src/js/features/comp/Cropper.ts           |  11 +-
 .../js/features/comp/EditorMarkdown.test.ts   |   2 +-
 web_src/js/features/comp/EditorMarkdown.ts    |   7 +-
 web_src/js/features/comp/EditorUpload.ts      |  11 +-
 web_src/js/features/comp/LabelEdit.ts         |  28 ++--
 web_src/js/features/comp/ReactionSelector.ts  |   9 +-
 web_src/js/features/comp/SearchUserBox.ts     |   2 +-
 web_src/js/features/comp/TextExpander.ts      |   3 +-
 web_src/js/features/comp/WebHookEditor.ts     |   9 +-
 web_src/js/features/copycontent.ts            |   2 +-
 web_src/js/features/dropzone.ts               |  17 +--
 .../js/features/eventsource.sharedworker.ts   |  15 +-
 web_src/js/features/file-view.ts              |   6 +-
 web_src/js/features/heatmap.ts                |   2 +-
 web_src/js/features/imagediff.ts              |  16 +--
 web_src/js/features/install.ts                |  56 ++++----
 web_src/js/features/notification.ts           |   6 +-
 web_src/js/features/oauth2-settings.ts        |   8 +-
 web_src/js/features/pull-view-file.ts         |  20 +--
 web_src/js/features/repo-branch.ts            |  18 +--
 web_src/js/features/repo-code.ts              |  22 +--
 web_src/js/features/repo-commit.ts            |   4 +-
 web_src/js/features/repo-common.ts            |  18 +--
 web_src/js/features/repo-diff-commit.ts       |  14 +-
 web_src/js/features/repo-diff.ts              |  41 +++---
 web_src/js/features/repo-editor.ts            |  36 ++---
 web_src/js/features/repo-graph.ts             |   6 +-
 web_src/js/features/repo-home.ts              |  20 +--
 web_src/js/features/repo-issue-content.ts     |   8 +-
 web_src/js/features/repo-issue-edit.ts        |  42 +++---
 web_src/js/features/repo-issue-list.ts        |  30 ++--
 web_src/js/features/repo-issue-pull.ts        |  16 +--
 .../features/repo-issue-sidebar-combolist.ts  |  18 +--
 web_src/js/features/repo-issue-sidebar.ts     |  12 +-
 web_src/js/features/repo-issue.ts             | 133 +++++++++---------
 web_src/js/features/repo-legacy.ts            |   4 +-
 web_src/js/features/repo-migrate.ts           |  10 +-
 web_src/js/features/repo-migration.ts         |   4 +-
 web_src/js/features/repo-milestone.ts         |   4 +-
 web_src/js/features/repo-new.ts               |  28 ++--
 web_src/js/features/repo-projects.ts          |  40 +++---
 web_src/js/features/repo-release.ts           |  18 +--
 web_src/js/features/repo-search.ts            |   6 +-
 .../features/repo-settings-branches.test.ts   |   6 +-
 web_src/js/features/repo-settings-branches.ts |   4 +-
 web_src/js/features/repo-settings.ts          |  32 ++---
 web_src/js/features/repo-unicode-escape.ts    |   4 +-
 web_src/js/features/repo-view-file-tree.ts    |   6 +-
 web_src/js/features/repo-wiki.ts              |   4 +-
 web_src/js/features/sshkey-helper.ts          |   2 +-
 web_src/js/features/tablesort.ts              |   6 +-
 web_src/js/features/user-auth-webauthn.ts     |  10 +-
 web_src/js/features/user-auth.ts              |   2 +-
 web_src/js/features/user-settings.ts          |   6 +-
 web_src/js/htmx.ts                            |   4 +-
 web_src/js/markup/anchors.ts                  |   4 +-
 web_src/js/markup/codecopy.ts                 |   2 +-
 web_src/js/markup/mermaid.ts                  |   2 +-
 web_src/js/markup/refissue.ts                 |   2 +-
 web_src/js/markup/render-iframe.ts            |   2 +-
 web_src/js/markup/tasklist.ts                 |  14 +-
 web_src/js/modules/diff-file.ts               |   4 +-
 web_src/js/modules/fetch.ts                   |   4 +-
 web_src/js/modules/fomantic/tab.ts            |   2 +-
 web_src/js/modules/observer.ts                |   4 +-
 web_src/js/modules/sortable.ts                |   4 +-
 web_src/js/modules/tippy.ts                   |   6 +-
 web_src/js/modules/toast.ts                   |   9 +-
 web_src/js/standalone/devtest.ts              |  10 +-
 .../js/standalone/external-render-iframe.ts   |   2 +-
 web_src/js/standalone/swagger.ts              |   2 +-
 web_src/js/types.ts                           |   2 +-
 web_src/js/utils.ts                           |  36 ++---
 web_src/js/utils/dom.test.ts                  |   6 +-
 web_src/js/utils/dom.ts                       |  25 ++--
 web_src/js/webcomponents/absolute-date.ts     |   8 +-
 web_src/js/webcomponents/origin-url.ts        |   2 +-
 web_src/js/webcomponents/overflow-menu.ts     |  12 +-
 108 files changed, 686 insertions(+), 658 deletions(-)

diff --git a/eslint.config.ts b/eslint.config.ts
index c849cdbc62..c2fddc856c 100644
--- a/eslint.config.ts
+++ b/eslint.config.ts
@@ -205,7 +205,7 @@ export default defineConfig([
       '@typescript-eslint/no-non-null-asserted-optional-chain': [2],
       '@typescript-eslint/no-non-null-assertion': [0],
       '@typescript-eslint/no-redeclare': [0],
-      '@typescript-eslint/no-redundant-type-constituents': [0], // rule does not properly work without strickNullChecks
+      '@typescript-eslint/no-redundant-type-constituents': [2],
       '@typescript-eslint/no-require-imports': [2],
       '@typescript-eslint/no-restricted-imports': [0],
       '@typescript-eslint/no-restricted-types': [0],
diff --git a/tsconfig.json b/tsconfig.json
index 1daf4b7233..2466faf592 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -40,7 +40,7 @@
     "strictBindCallApply": true,
     "strictBuiltinIteratorReturn": true,
     "strictFunctionTypes": true,
-    "strictNullChecks": false,
+    "strictNullChecks": true,
     "stripInternal": true,
     "verbatimModuleSyntax": true,
     "types": [
diff --git a/web_src/js/bootstrap.ts b/web_src/js/bootstrap.ts
index 4d3f39f5bf..a94e1d66b0 100644
--- a/web_src/js/bootstrap.ts
+++ b/web_src/js/bootstrap.ts
@@ -35,7 +35,7 @@ export function showGlobalErrorMessage(msg: string, msgType: Intent = 'error') {
   const msgCount = Number(msgDiv.getAttribute(`data-global-error-msg-count`)) + 1;
   msgDiv.setAttribute(`data-global-error-msg-compact`, msgCompact);
   msgDiv.setAttribute(`data-global-error-msg-count`, msgCount.toString());
-  msgDiv.querySelector('.ui.message').textContent = msg + (msgCount > 1 ? ` (${msgCount})` : '');
+  msgDiv.querySelector('.ui.message')!.textContent = msg + (msgCount > 1 ? ` (${msgCount})` : '');
   msgContainer.prepend(msgDiv);
 }
 
diff --git a/web_src/js/components/ActivityHeatmap.vue b/web_src/js/components/ActivityHeatmap.vue
index d805817630..7c7e0cd94c 100644
--- a/web_src/js/components/ActivityHeatmap.vue
+++ b/web_src/js/components/ActivityHeatmap.vue
@@ -5,7 +5,7 @@ import {onMounted, shallowRef} from 'vue';
 import type {Value as HeatmapValue, Locale as HeatmapLocale} from '@silverwind/vue3-calendar-heatmap';
 
 defineProps<{
-  values?: HeatmapValue[];
+  values: HeatmapValue[];
   locale: {
     textTotalContributions: string;
     heatMapLocale: Partial<HeatmapLocale>;
@@ -28,7 +28,7 @@ const endDate = shallowRef(new Date());
 
 onMounted(() => {
   // work around issue with first legend color being rendered twice and legend cut off
-  const legend = document.querySelector<HTMLElement>('.vch__external-legend-wrapper');
+  const legend = document.querySelector<HTMLElement>('.vch__external-legend-wrapper')!;
   legend.setAttribute('viewBox', '12 0 80 10');
   legend.style.marginRight = '-12px';
 });
diff --git a/web_src/js/components/ContextPopup.vue b/web_src/js/components/ContextPopup.vue
index 31db902adc..733144aae1 100644
--- a/web_src/js/components/ContextPopup.vue
+++ b/web_src/js/components/ContextPopup.vue
@@ -11,15 +11,17 @@ const props = defineProps<{
 }>();
 
 const loading = shallowRef(false);
-const issue = shallowRef<Issue>(null);
+const issue = shallowRef<Issue | null>(null);
 const renderedLabels = shallowRef('');
 const errorMessage = shallowRef('');
 
 const createdAt = computed(() => {
+  if (!issue?.value) return '';
   return new Date(issue.value.created_at).toLocaleDateString(undefined, {year: 'numeric', month: 'short', day: 'numeric'});
 });
 
 const body = computed(() => {
+  if (!issue?.value) return '';
   const body = issue.value.body.replace(/\n+/g, ' ');
   return body.length > 85 ? `${body.substring(0, 85)}…` : body;
 });
diff --git a/web_src/js/components/DashboardRepoList.vue b/web_src/js/components/DashboardRepoList.vue
index e938814ec6..e1f8475ea8 100644
--- a/web_src/js/components/DashboardRepoList.vue
+++ b/web_src/js/components/DashboardRepoList.vue
@@ -110,9 +110,9 @@ export default defineComponent({
   },
 
   mounted() {
-    const el = document.querySelector('#dashboard-repo-list');
+    const el = document.querySelector('#dashboard-repo-list')!;
     this.changeReposFilter(this.reposFilter);
-    fomanticQuery(el.querySelector('.ui.dropdown')).dropdown();
+    fomanticQuery(el.querySelector('.ui.dropdown')!).dropdown();
 
     this.textArchivedFilterTitles = {
       'archived': this.textShowOnlyArchived,
diff --git a/web_src/js/components/DiffCommitSelector.vue b/web_src/js/components/DiffCommitSelector.vue
index e9aa3c6744..fcc7af1fa0 100644
--- a/web_src/js/components/DiffCommitSelector.vue
+++ b/web_src/js/components/DiffCommitSelector.vue
@@ -23,7 +23,7 @@ type CommitListResult = {
 export default defineComponent({
   components: {SvgIcon},
   data: () => {
-    const el = document.querySelector('#diff-commit-select');
+    const el = document.querySelector('#diff-commit-select')!;
     return {
       menuVisible: false,
       isLoading: false,
@@ -35,7 +35,7 @@ export default defineComponent({
       mergeBase: el.getAttribute('data-merge-base'),
       commits: [] as Array<Commit>,
       hoverActivated: false,
-      lastReviewCommitSha: '',
+      lastReviewCommitSha: '' as string | null,
       uniqueIdMenu: generateElemId('diff-commit-selector-menu-'),
       uniqueIdShowAll: generateElemId('diff-commit-selector-show-all-'),
     };
@@ -165,7 +165,7 @@ export default defineComponent({
     },
     /** Called when user clicks on since last review */
     changesSinceLastReviewClick() {
-      window.location.assign(`${this.issueLink}/files/${this.lastReviewCommitSha}..${this.commits.at(-1).id}${this.queryParams}`);
+      window.location.assign(`${this.issueLink}/files/${this.lastReviewCommitSha}..${this.commits.at(-1)!.id}${this.queryParams}`);
     },
     /** Clicking on a single commit opens this specific commit */
     commitClicked(commitId: string, newWindow = false) {
@@ -193,7 +193,7 @@ export default defineComponent({
         // find all selected commits and generate a link
         const firstSelected = this.commits.findIndex((x) => x.selected);
         const lastSelected = this.commits.findLastIndex((x) => x.selected);
-        let beforeCommitID: string;
+        let beforeCommitID: string | null = null;
         if (firstSelected === 0) {
           beforeCommitID = this.mergeBase;
         } else {
@@ -204,7 +204,7 @@ export default defineComponent({
         if (firstSelected === lastSelected) {
           // if the start and end are the same, we show this single commit
           window.location.assign(`${this.issueLink}/commits/${afterCommitID}${this.queryParams}`);
-        } else if (beforeCommitID === this.mergeBase && afterCommitID === this.commits.at(-1).id) {
+        } else if (beforeCommitID === this.mergeBase && afterCommitID === this.commits.at(-1)!.id) {
           // if the first commit is selected and the last commit is selected, we show all commits
           window.location.assign(`${this.issueLink}/files${this.queryParams}`);
         } else {
diff --git a/web_src/js/components/DiffFileTree.vue b/web_src/js/components/DiffFileTree.vue
index 981d10c1c1..e2934b967e 100644
--- a/web_src/js/components/DiffFileTree.vue
+++ b/web_src/js/components/DiffFileTree.vue
@@ -12,14 +12,14 @@ const store = diffTreeStore();
 onMounted(() => {
   // Default to true if unset
   store.fileTreeIsVisible = localStorage.getItem(LOCAL_STORAGE_KEY) !== 'false';
-  document.querySelector('.diff-toggle-file-tree-button').addEventListener('click', toggleVisibility);
+  document.querySelector('.diff-toggle-file-tree-button')!.addEventListener('click', toggleVisibility);
 
   hashChangeListener();
   window.addEventListener('hashchange', hashChangeListener);
 });
 
 onUnmounted(() => {
-  document.querySelector('.diff-toggle-file-tree-button').removeEventListener('click', toggleVisibility);
+  document.querySelector('.diff-toggle-file-tree-button')!.removeEventListener('click', toggleVisibility);
   window.removeEventListener('hashchange', hashChangeListener);
 });
 
@@ -33,7 +33,7 @@ function expandSelectedFile() {
   if (store.selectedItem) {
     const box = document.querySelector(store.selectedItem);
     const folded = box?.getAttribute('data-folded') === 'true';
-    if (folded) setFileFolding(box, box.querySelector('.fold-file'), false);
+    if (folded) setFileFolding(box, box.querySelector('.fold-file')!, false);
   }
 }
 
@@ -48,10 +48,10 @@ function updateVisibility(visible: boolean) {
 }
 
 function updateState(visible: boolean) {
-  const btn = document.querySelector('.diff-toggle-file-tree-button');
+  const btn = document.querySelector('.diff-toggle-file-tree-button')!;
   const [toShow, toHide] = btn.querySelectorAll('.icon');
-  const tree = document.querySelector('#diff-file-tree');
-  const newTooltip = btn.getAttribute(visible ? 'data-hide-text' : 'data-show-text');
+  const tree = document.querySelector('#diff-file-tree')!;
+  const newTooltip = btn.getAttribute(visible ? 'data-hide-text' : 'data-show-text')!;
   btn.setAttribute('data-tooltip-content', newTooltip);
   toggleElem(tree, visible);
   toggleElem(toShow, !visible);
diff --git a/web_src/js/components/RepoActionView.vue b/web_src/js/components/RepoActionView.vue
index 00748ee9bb..357a2ba10e 100644
--- a/web_src/js/components/RepoActionView.vue
+++ b/web_src/js/components/RepoActionView.vue
@@ -402,7 +402,7 @@ export default defineComponent({
         }
 
         // auto-scroll to the last log line of the last step
-        let autoScrollJobStepElement: HTMLElement;
+        let autoScrollJobStepElement: HTMLElement | undefined;
         for (let stepIndex = 0; stepIndex < this.currentJob.steps.length; stepIndex++) {
           if (!autoScrollStepIndexes.get(stepIndex)) continue;
           autoScrollJobStepElement = this.getJobStepLogsContainer(stepIndex);
@@ -468,7 +468,7 @@ export default defineComponent({
       }
       const logLine = this.elStepsContainer().querySelector(selectedLogStep);
       if (!logLine) return;
-      logLine.querySelector<HTMLAnchorElement>('.line-num').click();
+      logLine.querySelector<HTMLAnchorElement>('.line-num')!.click();
     },
   },
 });
diff --git a/web_src/js/components/RepoActivityTopAuthors.vue b/web_src/js/components/RepoActivityTopAuthors.vue
index 5a925f9943..1d04fa5239 100644
--- a/web_src/js/components/RepoActivityTopAuthors.vue
+++ b/web_src/js/components/RepoActivityTopAuthors.vue
@@ -1,7 +1,7 @@
 <script lang="ts" setup>
 // @ts-expect-error - module exports no types
 import {VueBarGraph} from 'vue-bar-graph';
-import {computed, onMounted, shallowRef, useTemplateRef} from 'vue';
+import {computed, onMounted, shallowRef, useTemplateRef, type ShallowRef} from 'vue';
 
 const colors = shallowRef({
   barColor: 'green',
@@ -41,8 +41,8 @@ const graphWidth = computed(() => {
   return activityTopAuthors.length * 40;
 });
 
-const styleElement = useTemplateRef('styleElement');
-const altStyleElement = useTemplateRef('altStyleElement');
+const styleElement = useTemplateRef('styleElement') as Readonly<ShallowRef<HTMLDivElement>>;
+const altStyleElement = useTemplateRef('altStyleElement') as Readonly<ShallowRef<HTMLDivElement>>;
 
 onMounted(() => {
   const refStyle = window.getComputedStyle(styleElement.value);
diff --git a/web_src/js/components/RepoBranchTagSelector.vue b/web_src/js/components/RepoBranchTagSelector.vue
index a0bd975f57..cf530f99b9 100644
--- a/web_src/js/components/RepoBranchTagSelector.vue
+++ b/web_src/js/components/RepoBranchTagSelector.vue
@@ -20,7 +20,10 @@ type TabLoadingStates = Record<SelectedTab, '' | 'loading' | 'done'>
 export default defineComponent({
   components: {SvgIcon},
   props: {
-    elRoot: HTMLElement,
+    elRoot: {
+      type: HTMLElement,
+      required: true,
+    },
   },
   data() {
     const shouldShowTabBranches = this.elRoot.getAttribute('data-show-tab-branches') === 'true';
@@ -33,28 +36,28 @@ export default defineComponent({
       activeItemIndex: 0,
       tabLoadingStates: {} as TabLoadingStates,
 
-      textReleaseCompare: this.elRoot.getAttribute('data-text-release-compare'),
-      textBranches: this.elRoot.getAttribute('data-text-branches'),
-      textTags: this.elRoot.getAttribute('data-text-tags'),
-      textFilterBranch: this.elRoot.getAttribute('data-text-filter-branch'),
-      textFilterTag: this.elRoot.getAttribute('data-text-filter-tag'),
-      textDefaultBranchLabel: this.elRoot.getAttribute('data-text-default-branch-label'),
-      textCreateTag: this.elRoot.getAttribute('data-text-create-tag'),
-      textCreateBranch: this.elRoot.getAttribute('data-text-create-branch'),
-      textCreateRefFrom: this.elRoot.getAttribute('data-text-create-ref-from'),
-      textNoResults: this.elRoot.getAttribute('data-text-no-results'),
-      textViewAllBranches: this.elRoot.getAttribute('data-text-view-all-branches'),
-      textViewAllTags: this.elRoot.getAttribute('data-text-view-all-tags'),
+      textReleaseCompare: this.elRoot.getAttribute('data-text-release-compare')!,
+      textBranches: this.elRoot.getAttribute('data-text-branches')!,
+      textTags: this.elRoot.getAttribute('data-text-tags')!,
+      textFilterBranch: this.elRoot.getAttribute('data-text-filter-branch')!,
+      textFilterTag: this.elRoot.getAttribute('data-text-filter-tag')!,
+      textDefaultBranchLabel: this.elRoot.getAttribute('data-text-default-branch-label')!,
+      textCreateTag: this.elRoot.getAttribute('data-text-create-tag')!,
+      textCreateBranch: this.elRoot.getAttribute('data-text-create-branch')!,
+      textCreateRefFrom: this.elRoot.getAttribute('data-text-create-ref-from')!,
+      textNoResults: this.elRoot.getAttribute('data-text-no-results')!,
+      textViewAllBranches: this.elRoot.getAttribute('data-text-view-all-branches')!,
+      textViewAllTags: this.elRoot.getAttribute('data-text-view-all-tags')!,
 
-      currentRepoDefaultBranch: this.elRoot.getAttribute('data-current-repo-default-branch'),
-      currentRepoLink: this.elRoot.getAttribute('data-current-repo-link'),
-      currentTreePath: this.elRoot.getAttribute('data-current-tree-path'),
+      currentRepoDefaultBranch: this.elRoot.getAttribute('data-current-repo-default-branch')!,
+      currentRepoLink: this.elRoot.getAttribute('data-current-repo-link')!,
+      currentTreePath: this.elRoot.getAttribute('data-current-tree-path')!,
       currentRefType: this.elRoot.getAttribute('data-current-ref-type') as GitRefType,
-      currentRefShortName: this.elRoot.getAttribute('data-current-ref-short-name'),
+      currentRefShortName: this.elRoot.getAttribute('data-current-ref-short-name')!,
 
-      refLinkTemplate: this.elRoot.getAttribute('data-ref-link-template'),
-      refFormActionTemplate: this.elRoot.getAttribute('data-ref-form-action-template'),
-      dropdownFixedText: this.elRoot.getAttribute('data-dropdown-fixed-text'),
+      refLinkTemplate: this.elRoot.getAttribute('data-ref-link-template')!,
+      refFormActionTemplate: this.elRoot.getAttribute('data-ref-form-action-template')!,
+      dropdownFixedText: this.elRoot.getAttribute('data-dropdown-fixed-text')!,
       showTabBranches: shouldShowTabBranches,
       showTabTags: this.elRoot.getAttribute('data-show-tab-tags') === 'true',
       allowCreateNewRef: this.elRoot.getAttribute('data-allow-create-new-ref') === 'true',
@@ -92,7 +95,7 @@ export default defineComponent({
       }).length;
     },
     createNewRefFormActionUrl() {
-      return `${this.currentRepoLink}/branches/_new/${this.currentRefType}/${pathEscapeSegments(this.currentRefShortName)}`;
+      return `${this.currentRepoLink}/branches/_new/${this.currentRefType}/${pathEscapeSegments(this.currentRefShortName!)}`;
     },
   },
   watch: {
diff --git a/web_src/js/components/RepoContributors.vue b/web_src/js/components/RepoContributors.vue
index 08d63540e2..3122aa12d2 100644
--- a/web_src/js/components/RepoContributors.vue
+++ b/web_src/js/components/RepoContributors.vue
@@ -174,7 +174,7 @@ export default defineComponent({
         user.max_contribution_type = 0;
         const filteredWeeks = user.weeks.filter((week: Record<string, number>) => {
           const oneWeek = 7 * 24 * 60 * 60 * 1000;
-          if (week.week >= this.xAxisMin - oneWeek && week.week <= this.xAxisMax + oneWeek) {
+          if (week.week >= this.xAxisMin! - oneWeek && week.week <= this.xAxisMax! + oneWeek) {
             user.total_commits += week.commits;
             user.total_additions += week.additions;
             user.total_deletions += week.deletions;
@@ -238,8 +238,8 @@ export default defineComponent({
     },
 
     updateOtherCharts({chart}: {chart: Chart}, reset: boolean = false) {
-      const minVal = Number(chart.options.scales.x.min);
-      const maxVal = Number(chart.options.scales.x.max);
+      const minVal = Number(chart.options.scales?.x?.min);
+      const maxVal = Number(chart.options.scales?.x?.max);
       if (reset) {
         this.xAxisMin = this.xAxisStart;
         this.xAxisMax = this.xAxisEnd;
@@ -302,8 +302,8 @@ export default defineComponent({
         },
         scales: {
           x: {
-            min: this.xAxisMin,
-            max: this.xAxisMax,
+            min: this.xAxisMin ?? undefined,
+            max: this.xAxisMax ?? undefined,
             type: 'time',
             grid: {
               display: false,
@@ -334,7 +334,7 @@ export default defineComponent({
     <div class="ui header tw-flex tw-items-center tw-justify-between">
       <div>
         <relative-time
-          v-if="xAxisMin > 0"
+          v-if="xAxisMin && xAxisMin > 0"
           format="datetime"
           year="numeric"
           month="short"
@@ -346,7 +346,7 @@ export default defineComponent({
         </relative-time>
         {{ isLoading ? locale.loadingTitle : errorText ? locale.loadingTitleFailed: "-" }}
         <relative-time
-          v-if="xAxisMax > 0"
+          v-if="xAxisMax && xAxisMax > 0"
           format="datetime"
           year="numeric"
           month="short"
diff --git a/web_src/js/components/RepoFileSearch.vue b/web_src/js/components/RepoFileSearch.vue
index cbc1d50656..dd93de9850 100644
--- a/web_src/js/components/RepoFileSearch.vue
+++ b/web_src/js/components/RepoFileSearch.vue
@@ -1,10 +1,10 @@
 <script lang="ts" setup>
-import { ref, computed, watch, nextTick, useTemplateRef, onMounted, onUnmounted } from 'vue';
+import {ref, computed, watch, nextTick, useTemplateRef, onMounted, onUnmounted, type ShallowRef} from 'vue';
 import {generateElemId} from '../utils/dom.ts';
-import { GET } from '../modules/fetch.ts';
-import { filterRepoFilesWeighted } from '../features/repo-findfile.ts';
-import { pathEscapeSegments } from '../utils/url.ts';
-import { SvgIcon } from '../svg.ts';
+import {GET} from '../modules/fetch.ts';
+import {filterRepoFilesWeighted} from '../features/repo-findfile.ts';
+import {pathEscapeSegments} from '../utils/url.ts';
+import {SvgIcon} from '../svg.ts';
 import {throttle} from 'throttle-debounce';
 
 const props = defineProps({
@@ -15,8 +15,8 @@ const props = defineProps({
   placeholder: { type: String, required: true },
 });
 
-const refElemInput = useTemplateRef<HTMLInputElement>('searchInput');
-const refElemPopup = useTemplateRef<HTMLElement>('searchPopup');
+const refElemInput = useTemplateRef('searchInput') as Readonly<ShallowRef<HTMLInputElement>>;
+const refElemPopup = useTemplateRef('searchPopup') as Readonly<ShallowRef<HTMLDivElement>>;
 
 const searchQuery = ref('');
 const allFiles = ref<string[]>([]);
diff --git a/web_src/js/components/ViewFileTree.vue b/web_src/js/components/ViewFileTree.vue
index 1f90f92586..dc131383f6 100644
--- a/web_src/js/components/ViewFileTree.vue
+++ b/web_src/js/components/ViewFileTree.vue
@@ -1,9 +1,9 @@
 <script lang="ts" setup>
 import ViewFileTreeItem from './ViewFileTreeItem.vue';
-import {onMounted, useTemplateRef} from 'vue';
+import {onMounted, useTemplateRef, type ShallowRef} from 'vue';
 import {createViewFileTreeStore} from './ViewFileTreeStore.ts';
 
-const elRoot = useTemplateRef('elRoot');
+const elRoot = useTemplateRef('elRoot') as Readonly<ShallowRef<HTMLDivElement>>;;
 
 const props = defineProps({
   repoLink: {type: String, required: true},
@@ -24,7 +24,7 @@ onMounted(async () => {
 
 <template>
   <div class="view-file-tree-items" ref="elRoot">
-    <ViewFileTreeItem v-for="item in store.rootFiles" :key="item.name" :item="item" :store="store"/>
+    <ViewFileTreeItem v-for="item in store.rootFiles" :key="item.entryName" :item="item" :store="store"/>
   </div>
 </template>
 
diff --git a/web_src/js/components/ViewFileTreeItem.vue b/web_src/js/components/ViewFileTreeItem.vue
index 06d761dd65..9a50adedaa 100644
--- a/web_src/js/components/ViewFileTreeItem.vue
+++ b/web_src/js/components/ViewFileTreeItem.vue
@@ -4,7 +4,7 @@ import {isPlainClick} from '../utils/dom.ts';
 import {shallowRef} from 'vue';
 import {type createViewFileTreeStore} from './ViewFileTreeStore.ts';
 
-type Item = {
+export type Item = {
   entryName: string;
   entryMode: 'blob' | 'exec' | 'tree' | 'commit' | 'symlink' | 'unknown';
   entryIcon: string;
diff --git a/web_src/js/components/ViewFileTreeStore.ts b/web_src/js/components/ViewFileTreeStore.ts
index 61d9168aa6..211567d0a1 100644
--- a/web_src/js/components/ViewFileTreeStore.ts
+++ b/web_src/js/components/ViewFileTreeStore.ts
@@ -3,10 +3,11 @@ import {GET} from '../modules/fetch.ts';
 import {pathEscapeSegments} from '../utils/url.ts';
 import {createElementFromHTML} from '../utils/dom.ts';
 import {html} from '../utils/html.ts';
+import type {Item} from './ViewFileTreeItem.vue';
 
 export function createViewFileTreeStore(props: {repoLink: string, treePath: string, currentRefNameSubURL: string}) {
   const store = reactive({
-    rootFiles: [],
+    rootFiles: [] as Array<Item>,
     selectedItem: props.treePath,
 
     async loadChildren(treePath: string, subPath: string = '') {
@@ -28,7 +29,7 @@ export function createViewFileTreeStore(props: {repoLink: string, treePath: stri
       const u = new URL(url, window.origin);
       u.searchParams.set('only_content', 'true');
       const response = await GET(u.href);
-      const elViewContent = document.querySelector('.repo-view-content');
+      const elViewContent = document.querySelector('.repo-view-content')!;
       elViewContent.innerHTML = await response.text();
       const elViewContentData = elViewContent.querySelector('.repo-view-content-data');
       if (!elViewContentData) return; // if error occurs, there is no such element
@@ -39,7 +40,7 @@ export function createViewFileTreeStore(props: {repoLink: string, treePath: stri
 
     async navigateTreeView(treePath: string) {
       const url = store.buildTreePathWebUrl(treePath);
-      window.history.pushState({treePath, url}, null, url);
+      window.history.pushState({treePath, url}, '', url);
       store.selectedItem = treePath;
       await store.loadViewContent(url);
     },
diff --git a/web_src/js/features/admin/common.ts b/web_src/js/features/admin/common.ts
index dd5b1f464d..c019b80671 100644
--- a/web_src/js/features/admin/common.ts
+++ b/web_src/js/features/admin/common.ts
@@ -63,7 +63,7 @@ function initAdminAuthentication() {
 
   function onUsePagedSearchChange() {
     const searchPageSizeElements = document.querySelectorAll<HTMLDivElement>('.search-page-size');
-    if (document.querySelector<HTMLInputElement>('#use_paged_search').checked) {
+    if (document.querySelector<HTMLInputElement>('#use_paged_search')!.checked) {
       showElem('.search-page-size');
       for (const el of searchPageSizeElements) {
         el.querySelector('input')?.setAttribute('required', 'required');
@@ -82,10 +82,10 @@ function initAdminAuthentication() {
       input.removeAttribute('required');
     }
 
-    const provider = document.querySelector<HTMLInputElement>('#oauth2_provider').value;
+    const provider = document.querySelector<HTMLInputElement>('#oauth2_provider')!.value;
     switch (provider) {
       case 'openidConnect':
-        document.querySelector<HTMLInputElement>('.open_id_connect_auto_discovery_url input').setAttribute('required', 'required');
+        document.querySelector<HTMLInputElement>('.open_id_connect_auto_discovery_url input')!.setAttribute('required', 'required');
         showElem('.open_id_connect_auto_discovery_url');
         break;
       default: {
@@ -97,7 +97,7 @@ function initAdminAuthentication() {
           showElem('.oauth2_use_custom_url'); // show the checkbox
         }
         if (mustProvideCustomURLs) {
-          document.querySelector<HTMLInputElement>('#oauth2_use_custom_url').checked = true; // make the checkbox checked
+          document.querySelector<HTMLInputElement>('#oauth2_use_custom_url')!.checked = true; // make the checkbox checked
         }
         break;
       }
@@ -109,17 +109,17 @@ function initAdminAuthentication() {
   }
 
   function onOAuth2UseCustomURLChange(applyDefaultValues: boolean) {
-    const provider = document.querySelector<HTMLInputElement>('#oauth2_provider').value;
+    const provider = document.querySelector<HTMLInputElement>('#oauth2_provider')!.value;
     hideElem('.oauth2_use_custom_url_field');
     for (const input of document.querySelectorAll<HTMLInputElement>('.oauth2_use_custom_url_field input[required]')) {
       input.removeAttribute('required');
     }
 
     const elProviderCustomUrlSettings = document.querySelector(`#${provider}_customURLSettings`);
-    if (elProviderCustomUrlSettings && document.querySelector<HTMLInputElement>('#oauth2_use_custom_url').checked) {
+    if (elProviderCustomUrlSettings && document.querySelector<HTMLInputElement>('#oauth2_use_custom_url')!.checked) {
       for (const custom of ['token_url', 'auth_url', 'profile_url', 'email_url', 'tenant']) {
         if (applyDefaultValues) {
-          document.querySelector<HTMLInputElement>(`#oauth2_${custom}`).value = document.querySelector<HTMLInputElement>(`#${provider}_${custom}`).value;
+          document.querySelector<HTMLInputElement>(`#oauth2_${custom}`)!.value = document.querySelector<HTMLInputElement>(`#${provider}_${custom}`)!.value;
         }
         const customInput = document.querySelector(`#${provider}_${custom}`);
         if (customInput && customInput.getAttribute('data-available') === 'true') {
@@ -134,10 +134,10 @@ function initAdminAuthentication() {
 
   function onEnableLdapGroupsChange() {
     const checked = document.querySelector<HTMLInputElement>('.js-ldap-group-toggle')?.checked;
-    toggleElem(document.querySelector('#ldap-group-options'), checked);
+    toggleElem(document.querySelector('#ldap-group-options')!, checked);
   }
 
-  const elAuthType = document.querySelector<HTMLInputElement>('#auth_type');
+  const elAuthType = document.querySelector<HTMLInputElement>('#auth_type')!;
 
   // New authentication
   if (isNewPage) {
@@ -208,14 +208,14 @@ function initAdminAuthentication() {
     document.querySelector<HTMLInputElement>('#oauth2_provider')?.addEventListener('change', () => onOAuth2Change(true));
     document.querySelector<HTMLInputElement>('#oauth2_use_custom_url')?.addEventListener('change', () => onOAuth2UseCustomURLChange(true));
 
-    document.querySelector('.js-ldap-group-toggle').addEventListener('change', onEnableLdapGroupsChange);
+    document.querySelector('.js-ldap-group-toggle')!.addEventListener('change', onEnableLdapGroupsChange);
   }
   // Edit authentication
   if (isEditPage) {
     const authType = elAuthType.value;
     if (authType === '2' || authType === '5') {
       document.querySelector<HTMLInputElement>('#security_protocol')?.addEventListener('change', onSecurityProtocolChange);
-      document.querySelector('.js-ldap-group-toggle').addEventListener('change', onEnableLdapGroupsChange);
+      document.querySelector('.js-ldap-group-toggle')!.addEventListener('change', onEnableLdapGroupsChange);
       onEnableLdapGroupsChange();
       if (authType === '2') {
         document.querySelector<HTMLInputElement>('#use_paged_search')?.addEventListener('change', onUsePagedSearchChange);
@@ -227,10 +227,10 @@ function initAdminAuthentication() {
     }
   }
 
-  const elAuthName = document.querySelector<HTMLInputElement>('#auth_name');
+  const elAuthName = document.querySelector<HTMLInputElement>('#auth_name')!;
   const onAuthNameChange = function () {
     // appSubUrl is either empty or is a path that starts with `/` and doesn't have a trailing slash.
-    document.querySelector('#oauth2-callback-url').textContent = `${window.location.origin}${appSubUrl}/user/oauth2/${encodeURIComponent(elAuthName.value)}/callback`;
+    document.querySelector('#oauth2-callback-url')!.textContent = `${window.location.origin}${appSubUrl}/user/oauth2/${encodeURIComponent(elAuthName.value)}/callback`;
   };
   elAuthName.addEventListener('input', onAuthNameChange);
   onAuthNameChange();
@@ -240,13 +240,13 @@ function initAdminNotice() {
   const pageContent = document.querySelector('.page-content.admin.notice');
   if (!pageContent) return;
 
-  const detailModal = document.querySelector<HTMLDivElement>('#detail-modal');
+  const detailModal = document.querySelector<HTMLDivElement>('#detail-modal')!;
 
   // Attach view detail modals
   queryElems(pageContent, '.view-detail', (el) => el.addEventListener('click', (e) => {
     e.preventDefault();
-    const elNoticeDesc = el.closest('tr').querySelector('.notice-description');
-    const elModalDesc = detailModal.querySelector('.content pre');
+    const elNoticeDesc = el.closest('tr')!.querySelector('.notice-description')!;
+    const elModalDesc = detailModal.querySelector('.content pre')!;
     elModalDesc.textContent = elNoticeDesc.textContent;
     fomanticQuery(detailModal).modal('show');
   }));
@@ -280,10 +280,10 @@ function initAdminNotice() {
     const data = new FormData();
     for (const checkbox of checkboxes) {
       if (checkbox.checked) {
-        data.append('ids[]', checkbox.closest('.ui.checkbox').getAttribute('data-id'));
+        data.append('ids[]', checkbox.closest('.ui.checkbox')!.getAttribute('data-id')!);
       }
     }
-    await POST(this.getAttribute('data-link'), {data});
-    window.location.href = this.getAttribute('data-redirect');
+    await POST(this.getAttribute('data-link')!, {data});
+    window.location.href = this.getAttribute('data-redirect')!;
   });
 }
diff --git a/web_src/js/features/admin/config.ts b/web_src/js/features/admin/config.ts
index 16d7a2426f..76f7c1db50 100644
--- a/web_src/js/features/admin/config.ts
+++ b/web_src/js/features/admin/config.ts
@@ -11,7 +11,7 @@ export function initAdminConfigs(): void {
     el.addEventListener('change', async () => {
       try {
         const resp = await POST(`${appSubUrl}/-/admin/config`, {
-          data: new URLSearchParams({key: el.getAttribute('data-config-dyn-key'), value: String(el.checked)}),
+          data: new URLSearchParams({key: el.getAttribute('data-config-dyn-key')!, value: String(el.checked)}),
         });
         const json: Record<string, any> = await resp.json();
         if (json.errorMessage) throw new Error(json.errorMessage);
diff --git a/web_src/js/features/admin/selfcheck.ts b/web_src/js/features/admin/selfcheck.ts
index 9f53378b52..903eb15c87 100644
--- a/web_src/js/features/admin/selfcheck.ts
+++ b/web_src/js/features/admin/selfcheck.ts
@@ -7,7 +7,7 @@ export async function initAdminSelfCheck() {
   const elCheckByFrontend = document.querySelector('#self-check-by-frontend');
   if (!elCheckByFrontend) return;
 
-  const elContent = document.querySelector<HTMLDivElement>('.page-content.admin .admin-setting-content');
+  const elContent = document.querySelector<HTMLDivElement>('.page-content.admin .admin-setting-content')!;
 
   // send frontend self-check request
   const resp = await POST(`${appSubUrl}/-/admin/self_check`, {
@@ -27,5 +27,5 @@ export async function initAdminSelfCheck() {
 
   // only show the "no problem" if there is no visible "self-check-problem"
   const hasProblem = Boolean(elContent.querySelectorAll('.self-check-problem:not(.tw-hidden)').length);
-  toggleElem(elContent.querySelector('.self-check-no-problem'), !hasProblem);
+  toggleElem(elContent.querySelector('.self-check-no-problem')!, !hasProblem);
 }
diff --git a/web_src/js/features/captcha.ts b/web_src/js/features/captcha.ts
index df234d0e5c..f3d153a036 100644
--- a/web_src/js/features/captcha.ts
+++ b/web_src/js/features/captcha.ts
@@ -4,7 +4,7 @@ export async function initCaptcha() {
   const captchaEl = document.querySelector('#captcha');
   if (!captchaEl) return;
 
-  const siteKey = captchaEl.getAttribute('data-sitekey');
+  const siteKey = captchaEl.getAttribute('data-sitekey')!;
   const isDark = isDarkTheme();
 
   const params = {
@@ -43,7 +43,7 @@ export async function initCaptcha() {
 
       // @ts-expect-error TS2540: Cannot assign to 'INPUT_NAME' because it is a read-only property.
       mCaptcha.INPUT_NAME = 'm-captcha-response';
-      const instanceURL = captchaEl.getAttribute('data-instance-url');
+      const instanceURL = captchaEl.getAttribute('data-instance-url')!;
 
       new mCaptcha.default({
         siteKey: {
diff --git a/web_src/js/features/citation.ts b/web_src/js/features/citation.ts
index 3c9fe0afc8..d5ecb52e72 100644
--- a/web_src/js/features/citation.ts
+++ b/web_src/js/features/citation.ts
@@ -31,15 +31,15 @@ export async function initCitationFileCopyContent() {
 
   if (!pageData.citationFileContent) return;
 
-  const citationCopyApa = document.querySelector<HTMLButtonElement>('#citation-copy-apa');
-  const citationCopyBibtex = document.querySelector<HTMLButtonElement>('#citation-copy-bibtex');
+  const citationCopyApa = document.querySelector<HTMLButtonElement>('#citation-copy-apa')!;
+  const citationCopyBibtex = document.querySelector<HTMLButtonElement>('#citation-copy-bibtex')!;
   const inputContent = document.querySelector<HTMLInputElement>('#citation-copy-content');
 
   if ((!citationCopyApa && !citationCopyBibtex) || !inputContent) return;
 
   const updateUi = () => {
     const isBibtex = (localStorage.getItem('citation-copy-format') || defaultCitationFormat) === 'bibtex';
-    const copyContent = (isBibtex ? citationCopyBibtex : citationCopyApa).getAttribute('data-text');
+    const copyContent = (isBibtex ? citationCopyBibtex : citationCopyApa).getAttribute('data-text')!;
     inputContent.value = copyContent;
     citationCopyBibtex.classList.toggle('primary', isBibtex);
     citationCopyApa.classList.toggle('primary', !isBibtex);
diff --git a/web_src/js/features/clipboard.ts b/web_src/js/features/clipboard.ts
index 22c264d774..d5e3b55f95 100644
--- a/web_src/js/features/clipboard.ts
+++ b/web_src/js/features/clipboard.ts
@@ -1,7 +1,6 @@
 import {showTemporaryTooltip} from '../modules/tippy.ts';
 import {toAbsoluteUrl} from '../utils.ts';
 import {clippie} from 'clippie';
-import type {DOMEvent} from '../utils/dom.ts';
 
 const {copy_success, copy_error} = window.config.i18n;
 
@@ -10,15 +9,15 @@ const {copy_success, copy_error} = window.config.i18n;
 // - data-clipboard-target: Holds a selector for a <input> or <textarea> whose content is copied
 // - data-clipboard-text-type: When set to 'url' will convert relative to absolute urls
 export function initGlobalCopyToClipboardListener() {
-  document.addEventListener('click', async (e: DOMEvent<MouseEvent>) => {
-    const target = e.target.closest('[data-clipboard-text], [data-clipboard-target]');
+  document.addEventListener('click', async (e) => {
+    const target = (e.target as HTMLElement).closest('[data-clipboard-text], [data-clipboard-target]');
     if (!target) return;
 
     e.preventDefault();
 
     let text = target.getAttribute('data-clipboard-text');
     if (!text) {
-      text = document.querySelector<HTMLInputElement>(target.getAttribute('data-clipboard-target'))?.value;
+      text = document.querySelector<HTMLInputElement>(target.getAttribute('data-clipboard-target')!)?.value ?? null;
     }
 
     if (text && target.getAttribute('data-clipboard-text-type') === 'url') {
diff --git a/web_src/js/features/colorpicker.ts b/web_src/js/features/colorpicker.ts
index 66d1fcb72a..face4ef228 100644
--- a/web_src/js/features/colorpicker.ts
+++ b/web_src/js/features/colorpicker.ts
@@ -1,5 +1,4 @@
 import {createTippy} from '../modules/tippy.ts';
-import type {DOMEvent} from '../utils/dom.ts';
 import {registerGlobalInitFunc} from '../modules/observer.ts';
 
 export async function initColorPickers() {
@@ -25,7 +24,7 @@ function updatePicker(el: HTMLElement, newValue: string): void {
 }
 
 function initPicker(el: HTMLElement): void {
-  const input = el.querySelector('input');
+  const input = el.querySelector('input')!;
 
   const square = document.createElement('div');
   square.classList.add('preview-square');
@@ -39,9 +38,9 @@ function initPicker(el: HTMLElement): void {
     updateSquare(square, e.detail.value);
   });
 
-  input.addEventListener('input', (e: DOMEvent<Event, HTMLInputElement>) => {
-    updateSquare(square, e.target.value);
-    updatePicker(picker, e.target.value);
+  input.addEventListener('input', (e) => {
+    updateSquare(square, (e.target as HTMLInputElement).value);
+    updatePicker(picker, (e.target as HTMLInputElement).value);
   });
 
   createTippy(input, {
@@ -62,13 +61,13 @@ function initPicker(el: HTMLElement): void {
     input.dispatchEvent(new Event('input', {bubbles: true}));
     updateSquare(square, color);
   };
-  el.querySelector('.generate-random-color').addEventListener('click', () => {
+  el.querySelector('.generate-random-color')!.addEventListener('click', () => {
     const newValue = `#${Math.floor(Math.random() * 0xFFFFFF).toString(16).padStart(6, '0')}`;
     setSelectedColor(newValue);
   });
   for (const colorEl of el.querySelectorAll<HTMLElement>('.precolors .color')) {
-    colorEl.addEventListener('click', (e: DOMEvent<MouseEvent, HTMLAnchorElement>) => {
-      const newValue = e.target.getAttribute('data-color-hex');
+    colorEl.addEventListener('click', (e) => {
+      const newValue = (e.target as HTMLElement).getAttribute('data-color-hex')!;
       setSelectedColor(newValue);
     });
   }
diff --git a/web_src/js/features/common-button.ts b/web_src/js/features/common-button.ts
index b52238912b..72044d2d4e 100644
--- a/web_src/js/features/common-button.ts
+++ b/web_src/js/features/common-button.ts
@@ -27,7 +27,7 @@ export function initGlobalDeleteButton(): void {
       const dataObj = btn.dataset;
 
       const modalId = btn.getAttribute('data-modal-id');
-      const modal = document.querySelector(`.delete.modal${modalId ? `#${modalId}` : ''}`);
+      const modal = document.querySelector(`.delete.modal${modalId ? `#${modalId}` : ''}`)!;
 
       // set the modal "display name" by `data-name`
       const modalNameEl = modal.querySelector('.name');
@@ -37,7 +37,7 @@ export function initGlobalDeleteButton(): void {
       for (const [key, value] of Object.entries(dataObj)) {
         if (key.startsWith('data')) {
           const textEl = modal.querySelector(`.${key}`);
-          if (textEl) textEl.textContent = value;
+          if (textEl) textEl.textContent = value ?? null;
         }
       }
 
@@ -46,7 +46,7 @@ export function initGlobalDeleteButton(): void {
         onApprove: () => {
           // if `data-type="form"` exists, then submit the form by the selector provided by `data-form="..."`
           if (btn.getAttribute('data-type') === 'form') {
-            const formSelector = btn.getAttribute('data-form');
+            const formSelector = btn.getAttribute('data-form')!;
             const form = document.querySelector<HTMLFormElement>(formSelector);
             if (!form) throw new Error(`no form named ${formSelector} found`);
             modal.classList.add('is-loading'); // the form is not in the modal, so also add loading indicator to the modal
@@ -59,14 +59,14 @@ export function initGlobalDeleteButton(): void {
           const postData = new FormData();
           for (const [key, value] of Object.entries(dataObj)) {
             if (key.startsWith('data')) { // for data-data-xxx (HTML) -> dataXxx (form)
-              postData.append(key.slice(4), value);
+              postData.append(key.slice(4), String(value));
             }
             if (key === 'id') { // for data-id="..."
-              postData.append('id', value);
+              postData.append('id', String(value));
             }
           }
           (async () => {
-            const response = await POST(btn.getAttribute('data-url'), {data: postData});
+            const response = await POST(btn.getAttribute('data-url')!, {data: postData});
             if (response.ok) {
               const data = await response.json();
               window.location.href = data.redirect;
@@ -84,7 +84,7 @@ function onShowPanelClick(el: HTMLElement, e: MouseEvent) {
   // a '.show-panel' element can show a panel, by `data-panel="selector"`
   // if it has "toggle" class, it toggles the panel
   e.preventDefault();
-  const sel = el.getAttribute('data-panel');
+  const sel = el.getAttribute('data-panel')!;
   const elems = el.classList.contains('toggle') ? toggleElem(sel) : showElem(sel);
   for (const elem of elems) {
     if (isElemVisible(elem as HTMLElement)) {
@@ -103,7 +103,7 @@ function onHidePanelClick(el: HTMLElement, e: MouseEvent) {
   }
   sel = el.getAttribute('data-panel-closest');
   if (sel) {
-    hideElem((el.parentNode as HTMLElement).closest(sel));
+    hideElem((el.parentNode as HTMLElement).closest(sel)!);
     return;
   }
   throw new Error('no panel to hide'); // should never happen, otherwise there is a bug in code
@@ -141,7 +141,7 @@ function onShowModalClick(el: HTMLElement, e: MouseEvent) {
   // * Then, try to query 'target' as HTML tag
   // If there is a ".{prop-name}" part like "data-modal-form.action", the "form" element's "action" property will be set, the "prop-name" will be camel-cased to "propName".
   e.preventDefault();
-  const modalSelector = el.getAttribute('data-modal');
+  const modalSelector = el.getAttribute('data-modal')!;
   const elModal = document.querySelector(modalSelector);
   if (!elModal) throw new Error('no modal for this action');
 
diff --git a/web_src/js/features/common-fetch-action.ts b/web_src/js/features/common-fetch-action.ts
index 3ca361b6e2..0714de95c8 100644
--- a/web_src/js/features/common-fetch-action.ts
+++ b/web_src/js/features/common-fetch-action.ts
@@ -114,7 +114,7 @@ async function onLinkActionClick(el: HTMLElement, e: Event) {
   // If the "link-action" has "data-modal-confirm" attribute, a "confirm modal dialog" will be shown before taking action.
   // Attribute "data-modal-confirm" can be a modal element by "#the-modal-id", or a string content for the modal dialog.
   e.preventDefault();
-  const url = el.getAttribute('data-url');
+  const url = el.getAttribute('data-url')!;
   const doRequest = async () => {
     if ('disabled' in el) el.disabled = true; // el could be A or BUTTON, but "A" doesn't have the "disabled" attribute
     await fetchActionDoRequest(el, url, {method: el.getAttribute('data-link-action-method') || 'POST'});
diff --git a/web_src/js/features/common-form.ts b/web_src/js/features/common-form.ts
index 7321d80c44..fe201e2a01 100644
--- a/web_src/js/features/common-form.ts
+++ b/web_src/js/features/common-form.ts
@@ -1,6 +1,6 @@
 import {applyAreYouSure, initAreYouSure} from '../vendor/jquery.are-you-sure.ts';
 import {handleGlobalEnterQuickSubmit} from './comp/QuickSubmit.ts';
-import {queryElems, type DOMEvent} from '../utils/dom.ts';
+import {queryElems} from '../utils/dom.ts';
 import {initComboMarkdownEditor} from './comp/ComboMarkdownEditor.ts';
 
 export function initGlobalFormDirtyLeaveConfirm() {
@@ -13,14 +13,14 @@ export function initGlobalFormDirtyLeaveConfirm() {
 }
 
 export function initGlobalEnterQuickSubmit() {
-  document.addEventListener('keydown', (e: DOMEvent<KeyboardEvent>) => {
+  document.addEventListener('keydown', (e) => {
     if (e.key !== 'Enter') return;
     const hasCtrlOrMeta = ((e.ctrlKey || e.metaKey) && !e.altKey);
-    if (hasCtrlOrMeta && e.target.matches('textarea')) {
+    if (hasCtrlOrMeta && (e.target as HTMLElement).matches('textarea')) {
       if (handleGlobalEnterQuickSubmit(e.target as HTMLElement)) {
         e.preventDefault();
       }
-    } else if (e.target.matches('input') && !e.target.closest('form')) {
+    } else if ((e.target as HTMLElement).matches('input') && !(e.target as HTMLElement).closest('form')) {
       // input in a normal form could handle Enter key by default, so we only handle the input outside a form
       // eslint-disable-next-line unicorn/no-lonely-if
       if (handleGlobalEnterQuickSubmit(e.target as HTMLElement)) {
diff --git a/web_src/js/features/common-issue-list.ts b/web_src/js/features/common-issue-list.ts
index 037529bd10..8e6000f050 100644
--- a/web_src/js/features/common-issue-list.ts
+++ b/web_src/js/features/common-issue-list.ts
@@ -31,9 +31,9 @@ export function initCommonIssueListQuickGoto() {
   const goto = document.querySelector<HTMLElement>('#issue-list-quick-goto');
   if (!goto) return;
 
-  const form = goto.closest('form');
-  const input = form.querySelector<HTMLInputElement>('input[name=q]');
-  const repoLink = goto.getAttribute('data-repo-link');
+  const form = goto.closest('form')!;
+  const input = form.querySelector<HTMLInputElement>('input[name=q]')!;
+  const repoLink = goto.getAttribute('data-repo-link')!;
 
   form.addEventListener('submit', (e) => {
     // if there is no goto button, or the form is submitted by non-quick-goto elements, submit the form directly
@@ -44,7 +44,10 @@ export function initCommonIssueListQuickGoto() {
 
     // if there is a goto button, use its link
     e.preventDefault();
-    window.location.href = goto.getAttribute('data-issue-goto-link');
+    const link = goto.getAttribute('data-issue-goto-link');
+    if (link) {
+      window.location.href = link;
+    }
   });
 
   const onInput = async () => {
diff --git a/web_src/js/features/common-organization.ts b/web_src/js/features/common-organization.ts
index a1f19bedea..0e616134b9 100644
--- a/web_src/js/features/common-organization.ts
+++ b/web_src/js/features/common-organization.ts
@@ -7,7 +7,7 @@ export function initCommonOrganization() {
   }
 
   document.querySelector<HTMLInputElement>('.organization.settings.options #org_name')?.addEventListener('input', function () {
-    const nameChanged = this.value.toLowerCase() !== this.getAttribute('data-org-name').toLowerCase();
+    const nameChanged = this.value.toLowerCase() !== this.getAttribute('data-org-name')!.toLowerCase();
     toggleElem('#org-name-change-prompt', nameChanged);
   });
 
diff --git a/web_src/js/features/common-page.ts b/web_src/js/features/common-page.ts
index 9f0757491c..5ecc271c0b 100644
--- a/web_src/js/features/common-page.ts
+++ b/web_src/js/features/common-page.ts
@@ -25,7 +25,7 @@ function initFooterLanguageMenu() {
     const item = (e.target as HTMLElement).closest('.item');
     if (!item) return;
     e.preventDefault();
-    await GET(item.getAttribute('data-url'));
+    await GET(item.getAttribute('data-url')!);
     window.location.reload();
   });
 }
@@ -39,7 +39,7 @@ function initFooterThemeSelector() {
     apiSettings: {url: `${appSubUrl}/-/web-theme/list`, cache: false},
   });
   addDelegatedEventListener(elDropdown, 'click', '.menu > .item', async (el) => {
-    const themeName = el.getAttribute('data-value');
+    const themeName = el.getAttribute('data-value')!;
     await POST(`${appSubUrl}/-/web-theme/apply?theme=${encodeURIComponent(themeName)}`);
     window.location.reload();
   });
diff --git a/web_src/js/features/comp/ComboMarkdownEditor.ts b/web_src/js/features/comp/ComboMarkdownEditor.ts
index afa3957e21..9ceb087005 100644
--- a/web_src/js/features/comp/ComboMarkdownEditor.ts
+++ b/web_src/js/features/comp/ComboMarkdownEditor.ts
@@ -81,7 +81,7 @@ export class ComboMarkdownEditor {
   textareaMarkdownToolbar: HTMLElement;
   textareaAutosize: any;
 
-  dropzone: HTMLElement;
+  dropzone: HTMLElement | null;
   attachedDropzoneInst: any;
 
   previewMode: string;
@@ -105,7 +105,7 @@ export class ComboMarkdownEditor {
     await this.switchToUserPreference();
   }
 
-  applyEditorHeights(el: HTMLElement, heights: Heights) {
+  applyEditorHeights(el: HTMLElement, heights: Heights | undefined) {
     if (!heights) return;
     if (heights.minHeight) el.style.minHeight = heights.minHeight;
     if (heights.height) el.style.height = heights.height;
@@ -114,14 +114,14 @@ export class ComboMarkdownEditor {
 
   setupContainer() {
     this.supportEasyMDE = this.container.getAttribute('data-support-easy-mde') === 'true';
-    this.previewMode = this.container.getAttribute('data-content-mode');
-    this.previewUrl = this.container.getAttribute('data-preview-url');
-    this.previewContext = this.container.getAttribute('data-preview-context');
-    initTextExpander(this.container.querySelector('text-expander'));
+    this.previewMode = this.container.getAttribute('data-content-mode')!;
+    this.previewUrl = this.container.getAttribute('data-preview-url')!;
+    this.previewContext = this.container.getAttribute('data-preview-context')!;
+    initTextExpander(this.container.querySelector('text-expander')!);
   }
 
   setupTextarea() {
-    this.textarea = this.container.querySelector('.markdown-text-editor');
+    this.textarea = this.container.querySelector('.markdown-text-editor')!;
     this.textarea._giteaComboMarkdownEditor = this;
     this.textarea.id = generateElemId(`_combo_markdown_editor_`);
     this.textarea.addEventListener('input', () => triggerEditorContentChanged(this.container));
@@ -131,7 +131,7 @@ export class ComboMarkdownEditor {
       this.textareaAutosize = autosize(this.textarea, {viewportMarginBottom: 130});
     }
 
-    this.textareaMarkdownToolbar = this.container.querySelector('markdown-toolbar');
+    this.textareaMarkdownToolbar = this.container.querySelector('markdown-toolbar')!;
     this.textareaMarkdownToolbar.setAttribute('for', this.textarea.id);
     for (const el of this.textareaMarkdownToolbar.querySelectorAll('.markdown-toolbar-button')) {
       // upstream bug: The role code is never executed in base MarkdownButtonElement https://github.com/github/markdown-toolbar-element/issues/70
@@ -140,9 +140,9 @@ export class ComboMarkdownEditor {
       if (el.nodeName === 'BUTTON' && !el.getAttribute('type')) el.setAttribute('type', 'button');
     }
 
-    const monospaceButton = this.container.querySelector('.markdown-switch-monospace');
+    const monospaceButton = this.container.querySelector('.markdown-switch-monospace')!;
     const monospaceEnabled = localStorage?.getItem('markdown-editor-monospace') === 'true';
-    const monospaceText = monospaceButton.getAttribute(monospaceEnabled ? 'data-disable-text' : 'data-enable-text');
+    const monospaceText = monospaceButton.getAttribute(monospaceEnabled ? 'data-disable-text' : 'data-enable-text')!;
     monospaceButton.setAttribute('data-tooltip-content', monospaceText);
     monospaceButton.setAttribute('aria-checked', String(monospaceEnabled));
     monospaceButton.addEventListener('click', (e) => {
@@ -150,13 +150,13 @@ export class ComboMarkdownEditor {
       const enabled = localStorage?.getItem('markdown-editor-monospace') !== 'true';
       localStorage.setItem('markdown-editor-monospace', String(enabled));
       this.textarea.classList.toggle('tw-font-mono', enabled);
-      const text = monospaceButton.getAttribute(enabled ? 'data-disable-text' : 'data-enable-text');
+      const text = monospaceButton.getAttribute(enabled ? 'data-disable-text' : 'data-enable-text')!;
       monospaceButton.setAttribute('data-tooltip-content', text);
       monospaceButton.setAttribute('aria-checked', String(enabled));
     });
 
     if (this.supportEasyMDE) {
-      const easymdeButton = this.container.querySelector('.markdown-switch-easymde');
+      const easymdeButton = this.container.querySelector('.markdown-switch-easymde')!;
       easymdeButton.addEventListener('click', async (e) => {
         e.preventDefault();
         this.userPreferredEditor = 'easymde';
@@ -173,7 +173,7 @@ export class ComboMarkdownEditor {
   async setupDropzone() {
     const dropzoneParentContainer = this.container.getAttribute('data-dropzone-parent-container');
     if (!dropzoneParentContainer) return;
-    this.dropzone = this.container.closest(this.container.getAttribute('data-dropzone-parent-container'))?.querySelector('.dropzone');
+    this.dropzone = this.container.closest(this.container.getAttribute('data-dropzone-parent-container')!)?.querySelector('.dropzone') ?? null;
     if (!this.dropzone) return;
 
     this.attachedDropzoneInst = await initDropzone(this.dropzone);
@@ -212,13 +212,14 @@ export class ComboMarkdownEditor {
     // Fomantic Tab requires the "data-tab" to be globally unique.
     // So here it uses our defined "data-tab-for" and "data-tab-panel" to generate the "data-tab" attribute for Fomantic.
     const tabIdSuffix = generateElemId();
-    this.tabEditor = Array.from(tabs).find((tab) => tab.getAttribute('data-tab-for') === 'markdown-writer');
-    this.tabPreviewer = Array.from(tabs).find((tab) => tab.getAttribute('data-tab-for') === 'markdown-previewer');
+    const tabsArr = Array.from(tabs);
+    this.tabEditor = tabsArr.find((tab) => tab.getAttribute('data-tab-for') === 'markdown-writer')!;
+    this.tabPreviewer = tabsArr.find((tab) => tab.getAttribute('data-tab-for') === 'markdown-previewer')!;
     this.tabEditor.setAttribute('data-tab', `markdown-writer-${tabIdSuffix}`);
     this.tabPreviewer.setAttribute('data-tab', `markdown-previewer-${tabIdSuffix}`);
 
-    const panelEditor = this.container.querySelector('.ui.tab[data-tab-panel="markdown-writer"]');
-    const panelPreviewer = this.container.querySelector('.ui.tab[data-tab-panel="markdown-previewer"]');
+    const panelEditor = this.container.querySelector('.ui.tab[data-tab-panel="markdown-writer"]')!;
+    const panelPreviewer = this.container.querySelector('.ui.tab[data-tab-panel="markdown-previewer"]')!;
     panelEditor.setAttribute('data-tab', `markdown-writer-${tabIdSuffix}`);
     panelPreviewer.setAttribute('data-tab', `markdown-previewer-${tabIdSuffix}`);
 
@@ -254,8 +255,8 @@ export class ComboMarkdownEditor {
   }
 
   initMarkdownButtonTableAdd() {
-    const addTableButton = this.container.querySelector('.markdown-button-table-add');
-    const addTablePanel = this.container.querySelector('.markdown-add-table-panel');
+    const addTableButton = this.container.querySelector('.markdown-button-table-add')!;
+    const addTablePanel = this.container.querySelector('.markdown-add-table-panel')!;
     // here the tippy can't attach to the button because the button already owns a tippy for tooltip
     const addTablePanelTippy = createTippy(addTablePanel, {
       content: addTablePanel,
@@ -267,9 +268,9 @@ export class ComboMarkdownEditor {
     });
     addTableButton.addEventListener('click', () => addTablePanelTippy.show());
 
-    addTablePanel.querySelector('.ui.button.primary').addEventListener('click', () => {
-      let rows = parseInt(addTablePanel.querySelector<HTMLInputElement>('[name=rows]').value);
-      let cols = parseInt(addTablePanel.querySelector<HTMLInputElement>('[name=cols]').value);
+    addTablePanel.querySelector('.ui.button.primary')!.addEventListener('click', () => {
+      let rows = parseInt(addTablePanel.querySelector<HTMLInputElement>('[name=rows]')!.value);
+      let cols = parseInt(addTablePanel.querySelector<HTMLInputElement>('[name=cols]')!.value);
       rows = Math.max(1, Math.min(100, rows));
       cols = Math.max(1, Math.min(100, cols));
       textareaInsertText(this.textarea, `\n${this.generateMarkdownTable(rows, cols)}\n\n`);
@@ -360,7 +361,7 @@ export class ComboMarkdownEditor {
         }
       },
     });
-    this.applyEditorHeights(this.container.querySelector('.CodeMirror-scroll'), this.options.editorHeights);
+    this.applyEditorHeights(this.container.querySelector('.CodeMirror-scroll')!, this.options.editorHeights);
     await attachTribute(this.easyMDE.codemirror.getInputField());
     if (this.dropzone) {
       initEasyMDEPaste(this.easyMDE, this.dropzone);
@@ -401,10 +402,10 @@ export class ComboMarkdownEditor {
     }
   }
 
-  get userPreferredEditor() {
-    return window.localStorage.getItem(`markdown-editor-${this.previewMode ?? 'default'}`);
+  get userPreferredEditor(): string {
+    return window.localStorage.getItem(`markdown-editor-${this.previewMode ?? 'default'}`) || '';
   }
-  set userPreferredEditor(s) {
+  set userPreferredEditor(s: string) {
     window.localStorage.setItem(`markdown-editor-${this.previewMode ?? 'default'}`, s);
   }
 }
diff --git a/web_src/js/features/comp/Cropper.ts b/web_src/js/features/comp/Cropper.ts
index c7359a8a90..9fd48697fa 100644
--- a/web_src/js/features/comp/Cropper.ts
+++ b/web_src/js/features/comp/Cropper.ts
@@ -1,4 +1,4 @@
-import {showElem, type DOMEvent} from '../../utils/dom.ts';
+import {showElem} from '../../utils/dom.ts';
 
 type CropperOpts = {
   container: HTMLElement,
@@ -17,6 +17,7 @@ async function initCompCropper({container, fileInput, imageSource}: CropperOpts)
     crop() {
       const canvas = cropper.getCroppedCanvas();
       canvas.toBlob((blob) => {
+        if (!blob) return;
         const croppedFileName = currentFileName.replace(/\.[^.]{3,4}$/, '.png');
         const croppedFile = new File([blob], croppedFileName, {type: 'image/png', lastModified: currentFileLastModified});
         const dataTransfer = new DataTransfer();
@@ -26,9 +27,9 @@ async function initCompCropper({container, fileInput, imageSource}: CropperOpts)
     },
   });
 
-  fileInput.addEventListener('input', (e: DOMEvent<Event, HTMLInputElement>) => {
-    const files = e.target.files;
-    if (files?.length > 0) {
+  fileInput.addEventListener('input', (e) => {
+    const files = (e.target as HTMLInputElement).files;
+    if (files?.length) {
       currentFileName = files[0].name;
       currentFileLastModified = files[0].lastModified;
       const fileURL = URL.createObjectURL(files[0]);
@@ -42,6 +43,6 @@ async function initCompCropper({container, fileInput, imageSource}: CropperOpts)
 export async function initAvatarUploaderWithCropper(fileInput: HTMLInputElement) {
   const panel = fileInput.nextElementSibling as HTMLElement;
   if (!panel?.matches('.cropper-panel')) throw new Error('Missing cropper panel for avatar uploader');
-  const imageSource = panel.querySelector<HTMLImageElement>('.cropper-source');
+  const imageSource = panel.querySelector<HTMLImageElement>('.cropper-source')!;
   await initCompCropper({container: panel, fileInput, imageSource});
 }
diff --git a/web_src/js/features/comp/EditorMarkdown.test.ts b/web_src/js/features/comp/EditorMarkdown.test.ts
index ae3d0c9f0b..295a803015 100644
--- a/web_src/js/features/comp/EditorMarkdown.test.ts
+++ b/web_src/js/features/comp/EditorMarkdown.test.ts
@@ -24,7 +24,7 @@ test('textareaSplitLines', () => {
 });
 
 test('markdownHandleIndention', () => {
-  const testInput = (input: string, expected?: string) => {
+  const testInput = (input: string, expected: string | null) => {
     const inputPos = input.indexOf('|');
     input = input.replaceAll('|', '');
     const ret = markdownHandleIndention({value: input, selStart: inputPos, selEnd: inputPos});
diff --git a/web_src/js/features/comp/EditorMarkdown.ts b/web_src/js/features/comp/EditorMarkdown.ts
index 00cf4a188c..2240e2f41b 100644
--- a/web_src/js/features/comp/EditorMarkdown.ts
+++ b/web_src/js/features/comp/EditorMarkdown.ts
@@ -45,7 +45,8 @@ function handleIndentSelection(textarea: HTMLTextAreaElement, e: KeyboardEvent)
   }
 
   // re-calculating the selection range
-  let newSelStart, newSelEnd;
+  let newSelStart: number | null = null;
+  let newSelEnd: number | null = null;
   pos = 0;
   for (let i = 0; i < lines.length; i++) {
     if (i === selectedLines[0]) {
@@ -134,7 +135,7 @@ export function markdownHandleIndention(tvs: TextareaValueSelection): MarkdownHa
 
   // parse the indention
   let lineContent = line;
-  const indention = /^\s*/.exec(lineContent)[0];
+  const indention = (/^\s*/.exec(lineContent) || [''])[0];
   lineContent = lineContent.slice(indention.length);
   if (linesBuf.inlinePos <= indention.length) return unhandled; // if cursor is at the indention, do nothing, let the browser handle it
 
@@ -177,7 +178,7 @@ export function markdownHandleIndention(tvs: TextareaValueSelection): MarkdownHa
 
 function handleNewline(textarea: HTMLTextAreaElement, e: Event) {
   const ret = markdownHandleIndention({value: textarea.value, selStart: textarea.selectionStart, selEnd: textarea.selectionEnd});
-  if (!ret.handled) return;
+  if (!ret.handled || !ret.valueSelection) return; // FIXME: the "handled" seems redundant, only valueSelection is enough (null for unhandled)
   e.preventDefault();
   textarea.value = ret.valueSelection.value;
   textarea.setSelectionRange(ret.valueSelection.selStart, ret.valueSelection.selEnd);
diff --git a/web_src/js/features/comp/EditorUpload.ts b/web_src/js/features/comp/EditorUpload.ts
index 3e4a84568c..92593e7092 100644
--- a/web_src/js/features/comp/EditorUpload.ts
+++ b/web_src/js/features/comp/EditorUpload.ts
@@ -121,7 +121,10 @@ function getPastedImages(e: ClipboardEvent) {
   const images: Array<File> = [];
   for (const item of e.clipboardData?.items ?? []) {
     if (item.type?.startsWith('image/')) {
-      images.push(item.getAsFile());
+      const file = item.getAsFile();
+      if (file) {
+        images.push(file);
+      }
     }
   }
   return images;
@@ -135,7 +138,7 @@ export function initEasyMDEPaste(easyMDE: EasyMDE, dropzoneEl: HTMLElement) {
     handleUploadFiles(editor, dropzoneEl, images, e);
   });
   easyMDE.codemirror.on('drop', (_, e) => {
-    if (!e.dataTransfer.files.length) return;
+    if (!e.dataTransfer?.files.length) return;
     handleUploadFiles(editor, dropzoneEl, e.dataTransfer.files, e);
   });
   dropzoneEl.dropzone.on(DropzoneCustomEventRemovedFile, ({fileUuid}) => {
@@ -145,7 +148,7 @@ export function initEasyMDEPaste(easyMDE: EasyMDE, dropzoneEl: HTMLElement) {
   });
 }
 
-export function initTextareaEvents(textarea: HTMLTextAreaElement, dropzoneEl: HTMLElement) {
+export function initTextareaEvents(textarea: HTMLTextAreaElement, dropzoneEl: HTMLElement | null) {
   subscribe(textarea); // enable paste features
   textarea.addEventListener('paste', (e: ClipboardEvent) => {
     const images = getPastedImages(e);
@@ -154,7 +157,7 @@ export function initTextareaEvents(textarea: HTMLTextAreaElement, dropzoneEl: HT
     }
   });
   textarea.addEventListener('drop', (e: DragEvent) => {
-    if (!e.dataTransfer.files.length) return;
+    if (!e.dataTransfer?.files.length) return;
     if (!dropzoneEl) return;
     handleUploadFiles(new TextareaEditor(textarea), dropzoneEl, e.dataTransfer.files, e);
   });
diff --git a/web_src/js/features/comp/LabelEdit.ts b/web_src/js/features/comp/LabelEdit.ts
index 3e27eac1c5..59cb49d4a3 100644
--- a/web_src/js/features/comp/LabelEdit.ts
+++ b/web_src/js/features/comp/LabelEdit.ts
@@ -14,17 +14,17 @@ export function initCompLabelEdit(pageSelector: string) {
   const elModal = pageContent.querySelector<HTMLElement>('#issue-label-edit-modal');
   if (!elModal) return;
 
-  const elLabelId = elModal.querySelector<HTMLInputElement>('input[name="id"]');
-  const elNameInput = elModal.querySelector<HTMLInputElement>('.label-name-input');
-  const elExclusiveField = elModal.querySelector('.label-exclusive-input-field');
-  const elExclusiveInput = elModal.querySelector<HTMLInputElement>('.label-exclusive-input');
-  const elExclusiveWarning = elModal.querySelector('.label-exclusive-warning');
-  const elExclusiveOrderField = elModal.querySelector<HTMLInputElement>('.label-exclusive-order-input-field');
-  const elExclusiveOrderInput = elModal.querySelector<HTMLInputElement>('.label-exclusive-order-input');
-  const elIsArchivedField = elModal.querySelector('.label-is-archived-input-field');
-  const elIsArchivedInput = elModal.querySelector<HTMLInputElement>('.label-is-archived-input');
-  const elDescInput = elModal.querySelector<HTMLInputElement>('.label-desc-input');
-  const elColorInput = elModal.querySelector<HTMLInputElement>('.color-picker-combo input');
+  const elLabelId = elModal.querySelector<HTMLInputElement>('input[name="id"]')!;
+  const elNameInput = elModal.querySelector<HTMLInputElement>('.label-name-input')!;
+  const elExclusiveField = elModal.querySelector('.label-exclusive-input-field')!;
+  const elExclusiveInput = elModal.querySelector<HTMLInputElement>('.label-exclusive-input')!;
+  const elExclusiveWarning = elModal.querySelector('.label-exclusive-warning')!;
+  const elExclusiveOrderField = elModal.querySelector<HTMLInputElement>('.label-exclusive-order-input-field')!;
+  const elExclusiveOrderInput = elModal.querySelector<HTMLInputElement>('.label-exclusive-order-input')!;
+  const elIsArchivedField = elModal.querySelector('.label-is-archived-input-field')!;
+  const elIsArchivedInput = elModal.querySelector<HTMLInputElement>('.label-is-archived-input')!;
+  const elDescInput = elModal.querySelector<HTMLInputElement>('.label-desc-input')!;
+  const elColorInput = elModal.querySelector<HTMLInputElement>('.color-picker-combo input')!;
 
   const syncModalUi = () => {
     const hasScope = nameHasScope(elNameInput.value);
@@ -37,13 +37,13 @@ export function initCompLabelEdit(pageSelector: string) {
     if (parseInt(elExclusiveOrderInput.value) <= 0) {
       elExclusiveOrderInput.style.color = 'var(--color-placeholder-text) !important';
     } else {
-      elExclusiveOrderInput.style.color = null;
+      elExclusiveOrderInput.style.removeProperty('color');
     }
   };
 
   const showLabelEditModal = (btn:HTMLElement) => {
     // the "btn" should contain the label's attributes by its `data-label-xxx` attributes
-    const form = elModal.querySelector<HTMLFormElement>('form');
+    const form = elModal.querySelector<HTMLFormElement>('form')!;
     elLabelId.value = btn.getAttribute('data-label-id') || '';
     elNameInput.value = btn.getAttribute('data-label-name') || '';
     elExclusiveOrderInput.value = btn.getAttribute('data-label-exclusive-order') || '0';
@@ -59,7 +59,7 @@ export function initCompLabelEdit(pageSelector: string) {
     // if a label was not exclusive but has issues, then it should warn user if it will become exclusive
     const numIssues = parseInt(btn.getAttribute('data-label-num-issues') || '0');
     elModal.toggleAttribute('data-need-warn-exclusive', !elExclusiveInput.checked && numIssues > 0);
-    elModal.querySelector('.header').textContent = isEdit ? elModal.getAttribute('data-text-edit-label') : elModal.getAttribute('data-text-new-label');
+    elModal.querySelector('.header')!.textContent = isEdit ? elModal.getAttribute('data-text-edit-label') : elModal.getAttribute('data-text-new-label');
 
     const curPageLink = elModal.getAttribute('data-current-page-link');
     form.action = isEdit ? `${curPageLink}/edit` : `${curPageLink}/new`;
diff --git a/web_src/js/features/comp/ReactionSelector.ts b/web_src/js/features/comp/ReactionSelector.ts
index bb54593f11..efc592597a 100644
--- a/web_src/js/features/comp/ReactionSelector.ts
+++ b/web_src/js/features/comp/ReactionSelector.ts
@@ -1,18 +1,17 @@
 import {POST} from '../../modules/fetch.ts';
-import type {DOMEvent} from '../../utils/dom.ts';
 import {registerGlobalEventFunc} from '../../modules/observer.ts';
 
 export function initCompReactionSelector() {
-  registerGlobalEventFunc('click', 'onCommentReactionButtonClick', async (target: HTMLElement, e: DOMEvent<MouseEvent>) => {
+  registerGlobalEventFunc('click', 'onCommentReactionButtonClick', async (target: HTMLElement, e: Event) => {
     // there are 2 places for the "reaction" buttons, one is the top-right reaction menu, one is the bottom of the comment
     e.preventDefault();
 
     if (target.classList.contains('disabled')) return;
 
-    const actionUrl = target.closest('[data-action-url]').getAttribute('data-action-url');
-    const reactionContent = target.getAttribute('data-reaction-content');
+    const actionUrl = target.closest('[data-action-url]')!.getAttribute('data-action-url');
+    const reactionContent = target.getAttribute('data-reaction-content')!;
 
-    const commentContainer = target.closest('.comment-container');
+    const commentContainer = target.closest('.comment-container')!;
 
     const bottomReactions = commentContainer.querySelector('.bottom-reactions'); // may not exist if there is no reaction
     const bottomReactionBtn = bottomReactions?.querySelector(`a[data-reaction-content="${CSS.escape(reactionContent)}"]`);
diff --git a/web_src/js/features/comp/SearchUserBox.ts b/web_src/js/features/comp/SearchUserBox.ts
index 9cba18b356..f5680078a3 100644
--- a/web_src/js/features/comp/SearchUserBox.ts
+++ b/web_src/js/features/comp/SearchUserBox.ts
@@ -17,7 +17,7 @@ export function initCompSearchUserBox() {
       url: `${appSubUrl}/user/search_candidates?q={query}&orgs=${includeOrgs}`,
       onResponse(response: any) {
         const resultItems = [];
-        const searchQuery = searchUserBox.querySelector('input').value;
+        const searchQuery = searchUserBox.querySelector('input')!.value;
         const searchQueryUppercase = searchQuery.toUpperCase();
         for (const item of response.data) {
           const resultItem = {
diff --git a/web_src/js/features/comp/TextExpander.ts b/web_src/js/features/comp/TextExpander.ts
index 2d79fe5029..4a04a4422f 100644
--- a/web_src/js/features/comp/TextExpander.ts
+++ b/web_src/js/features/comp/TextExpander.ts
@@ -37,7 +37,7 @@ async function fetchIssueSuggestions(key: string, text: string): Promise<TextExp
 export function initTextExpander(expander: TextExpanderElement) {
   if (!expander) return;
 
-  const textarea = expander.querySelector<HTMLTextAreaElement>('textarea');
+  const textarea = expander.querySelector<HTMLTextAreaElement>('textarea')!;
 
   // help to fix the text-expander "multiword+promise" bug: do not show the popup when there is no "#" before current line
   const shouldShowIssueSuggestions = () => {
@@ -64,6 +64,7 @@ export function initTextExpander(expander: TextExpanderElement) {
   }, 300); // to match onInputDebounce delay
 
   expander.addEventListener('text-expander-change', (e: TextExpanderChangeEvent) => {
+    if (!e.detail) return;
     const {key, text, provide} = e.detail;
     if (key === ':') {
       const matches = matchEmoji(text);
diff --git a/web_src/js/features/comp/WebHookEditor.ts b/web_src/js/features/comp/WebHookEditor.ts
index 794b3c99ca..a69d438ba2 100644
--- a/web_src/js/features/comp/WebHookEditor.ts
+++ b/web_src/js/features/comp/WebHookEditor.ts
@@ -27,7 +27,7 @@ export function initCompWebHookEditor() {
   if (httpMethodInput) {
     const updateContentType = function () {
       const visible = httpMethodInput.value === 'POST';
-      toggleElem(document.querySelector('#content_type').closest('.field'), visible);
+      toggleElem(document.querySelector('#content_type')!.closest('.field')!, visible);
     };
     updateContentType();
     httpMethodInput.addEventListener('change', updateContentType);
@@ -36,9 +36,12 @@ export function initCompWebHookEditor() {
   // Test delivery
   document.querySelector<HTMLButtonElement>('#test-delivery')?.addEventListener('click', async function () {
     this.classList.add('is-loading', 'disabled');
-    await POST(this.getAttribute('data-link'));
+    await POST(this.getAttribute('data-link')!);
     setTimeout(() => {
-      window.location.href = this.getAttribute('data-redirect');
+      const redirectUrl = this.getAttribute('data-redirect');
+      if (redirectUrl) {
+        window.location.href = redirectUrl;
+      }
     }, 5000);
   });
 }
diff --git a/web_src/js/features/copycontent.ts b/web_src/js/features/copycontent.ts
index 0fec2a6235..74e98cf95e 100644
--- a/web_src/js/features/copycontent.ts
+++ b/web_src/js/features/copycontent.ts
@@ -20,7 +20,7 @@ export function initCopyContent() {
       btn.classList.add('is-loading', 'loading-icon-2px');
       try {
         const res = await GET(rawFileLink, {credentials: 'include', redirect: 'follow'});
-        const contentType = res.headers.get('content-type');
+        const contentType = res.headers.get('content-type')!;
 
         if (contentType.startsWith('image/') && !contentType.startsWith('image/svg')) {
           isRasterImage = true;
diff --git a/web_src/js/features/dropzone.ts b/web_src/js/features/dropzone.ts
index 508b7cb606..b86ed520f5 100644
--- a/web_src/js/features/dropzone.ts
+++ b/web_src/js/features/dropzone.ts
@@ -28,7 +28,7 @@ async function createDropzone(el: HTMLElement, opts: DropzoneOptions) {
 export function generateMarkdownLinkForAttachment(file: Partial<CustomDropzoneFile>, {width, dppx}: {width?: number, dppx?: number} = {}) {
   let fileMarkdown = `[${file.name}](/attachments/${file.uuid})`;
   if (isImageFile(file)) {
-    if (width > 0 && dppx > 1) {
+    if (width && width > 0 && dppx && dppx > 1) {
       // Scale down images from HiDPI monitors. This uses the <img> tag because it's the only
       // method to change image size in Markdown that is supported by all implementations.
       // Make the image link relative to the repo path, then the final URL is "/sub-path/owner/repo/attachments/{uuid}"
@@ -56,7 +56,7 @@ function addCopyLink(file: Partial<CustomDropzoneFile>) {
     const success = await clippie(generateMarkdownLinkForAttachment(file));
     showTemporaryTooltip(e.target as Element, success ? i18n.copy_success : i18n.copy_error);
   });
-  file.previewTemplate.append(copyLinkEl);
+  file.previewTemplate!.append(copyLinkEl);
 }
 
 type FileUuidDict = Record<string, {submitted: boolean}>;
@@ -66,15 +66,15 @@ type FileUuidDict = Record<string, {submitted: boolean}>;
  */
 export async function initDropzone(dropzoneEl: HTMLElement) {
   const listAttachmentsUrl = dropzoneEl.closest('[data-attachment-url]')?.getAttribute('data-attachment-url');
-  const removeAttachmentUrl = dropzoneEl.getAttribute('data-remove-url');
-  const attachmentBaseLinkUrl = dropzoneEl.getAttribute('data-link-url');
+  const removeAttachmentUrl = dropzoneEl.getAttribute('data-remove-url')!;
+  const attachmentBaseLinkUrl = dropzoneEl.getAttribute('data-link-url')!;
 
   let disableRemovedfileEvent = false; // when resetting the dropzone (removeAllFiles), disable the "removedfile" event
   let fileUuidDict: FileUuidDict = {}; // to record: if a comment has been saved, then the uploaded files won't be deleted from server when clicking the Remove in the dropzone
   const opts: Record<string, any> = {
     url: dropzoneEl.getAttribute('data-upload-url'),
     headers: {'X-Csrf-Token': csrfToken},
-    acceptedFiles: ['*/*', ''].includes(dropzoneEl.getAttribute('data-accepts')) ? null : dropzoneEl.getAttribute('data-accepts'),
+    acceptedFiles: ['*/*', ''].includes(dropzoneEl.getAttribute('data-accepts')!) ? null : dropzoneEl.getAttribute('data-accepts'),
     addRemoveLinks: true,
     dictDefaultMessage: dropzoneEl.getAttribute('data-default-message'),
     dictInvalidFileType: dropzoneEl.getAttribute('data-invalid-input-type'),
@@ -96,7 +96,7 @@ export async function initDropzone(dropzoneEl: HTMLElement) {
     file.uuid = resp.uuid;
     fileUuidDict[file.uuid] = {submitted: false};
     const input = createElementFromAttrs('input', {name: 'files', type: 'hidden', id: `dropzone-file-${resp.uuid}`, value: resp.uuid});
-    dropzoneEl.querySelector('.files').append(input);
+    dropzoneEl.querySelector('.files')!.append(input);
     addCopyLink(file);
     dzInst.emit(DropzoneCustomEventUploadDone, {file});
   });
@@ -120,6 +120,7 @@ export async function initDropzone(dropzoneEl: HTMLElement) {
 
   dzInst.on(DropzoneCustomEventReloadFiles, async () => {
     try {
+      if (!listAttachmentsUrl) return;
       const resp = await GET(listAttachmentsUrl);
       const respData = await resp.json();
       // do not trigger the "removedfile" event, otherwise the attachments would be deleted from server
@@ -127,7 +128,7 @@ export async function initDropzone(dropzoneEl: HTMLElement) {
       dzInst.removeAllFiles(true);
       disableRemovedfileEvent = false;
 
-      dropzoneEl.querySelector('.files').innerHTML = '';
+      dropzoneEl.querySelector('.files')!.innerHTML = '';
       for (const el of dropzoneEl.querySelectorAll('.dz-preview')) el.remove();
       fileUuidDict = {};
       for (const attachment of respData) {
@@ -141,7 +142,7 @@ export async function initDropzone(dropzoneEl: HTMLElement) {
         addCopyLink(file); // it is from server response, so no "type"
         fileUuidDict[file.uuid] = {submitted: true};
         const input = createElementFromAttrs('input', {name: 'files', type: 'hidden', id: `dropzone-file-${file.uuid}`, value: file.uuid});
-        dropzoneEl.querySelector('.files').append(input);
+        dropzoneEl.querySelector('.files')!.append(input);
       }
       if (!dropzoneEl.querySelector('.dz-preview')) {
         dropzoneEl.classList.remove('dz-started');
diff --git a/web_src/js/features/eventsource.sharedworker.ts b/web_src/js/features/eventsource.sharedworker.ts
index cfc31e111f..af52abc5a9 100644
--- a/web_src/js/features/eventsource.sharedworker.ts
+++ b/web_src/js/features/eventsource.sharedworker.ts
@@ -1,6 +1,6 @@
 class Source {
   url: string;
-  eventSource: EventSource;
+  eventSource: EventSource | null;
   listening: Record<string, boolean>;
   clients: Array<MessagePort>;
 
@@ -47,7 +47,7 @@ class Source {
   listen(eventType: string) {
     if (this.listening[eventType]) return;
     this.listening[eventType] = true;
-    this.eventSource.addEventListener(eventType, (event) => {
+    this.eventSource?.addEventListener(eventType, (event) => {
       this.notifyClients({
         type: eventType,
         data: event.data,
@@ -64,7 +64,7 @@ class Source {
   status(port: MessagePort) {
     port.postMessage({
       type: 'status',
-      message: `url: ${this.url} readyState: ${this.eventSource.readyState}`,
+      message: `url: ${this.url} readyState: ${this.eventSource?.readyState}`,
     });
   }
 }
@@ -85,14 +85,14 @@ self.addEventListener('connect', (e: MessageEvent) => {
       }
       if (event.data.type === 'start') {
         const url = event.data.url;
-        if (sourcesByUrl.get(url)) {
+        let source = sourcesByUrl.get(url);
+        if (source) {
           // we have a Source registered to this url
-          const source = sourcesByUrl.get(url);
           source.register(port);
           sourcesByPort.set(port, source);
           return;
         }
-        let source = sourcesByPort.get(port);
+        source = sourcesByPort.get(port);
         if (source) {
           if (source.eventSource && source.url === url) return;
 
@@ -111,11 +111,10 @@ self.addEventListener('connect', (e: MessageEvent) => {
         sourcesByUrl.set(url, source);
         sourcesByPort.set(port, source);
       } else if (event.data.type === 'listen') {
-        const source = sourcesByPort.get(port);
+        const source = sourcesByPort.get(port)!;
         source.listen(event.data.eventType);
       } else if (event.data.type === 'close') {
         const source = sourcesByPort.get(port);
-
         if (!source) return;
 
         const count = source.deregister(port);
diff --git a/web_src/js/features/file-view.ts b/web_src/js/features/file-view.ts
index 67f4381468..ff9e8cfa26 100644
--- a/web_src/js/features/file-view.ts
+++ b/web_src/js/features/file-view.ts
@@ -18,11 +18,11 @@ function findFileRenderPlugin(filename: string, mimeType: string): FileRenderPlu
 }
 
 function showRenderRawFileButton(elFileView: HTMLElement, renderContainer: HTMLElement | null): void {
-  const toggleButtons = elFileView.querySelector('.file-view-toggle-buttons');
+  const toggleButtons = elFileView.querySelector('.file-view-toggle-buttons')!;
   showElem(toggleButtons);
   const displayingRendered = Boolean(renderContainer);
   toggleElemClass(toggleButtons.querySelectorAll('.file-view-toggle-source'), 'active', !displayingRendered); // it may not exist
-  toggleElemClass(toggleButtons.querySelector('.file-view-toggle-rendered'), 'active', displayingRendered);
+  toggleElemClass(toggleButtons.querySelector('.file-view-toggle-rendered')!, 'active', displayingRendered);
   // TODO: if there is only one button, hide it?
 }
 
@@ -62,7 +62,7 @@ async function renderRawFileToContainer(container: HTMLElement, rawFileLink: str
 export function initRepoFileView(): void {
   registerGlobalInitFunc('initRepoFileView', async (elFileView: HTMLElement) => {
     initPluginsOnce();
-    const rawFileLink = elFileView.getAttribute('data-raw-file-link');
+    const rawFileLink = elFileView.getAttribute('data-raw-file-link')!;
     const mimeType = elFileView.getAttribute('data-mime-type') || ''; // not used yet
     // TODO: we should also provide the prefetched file head bytes to let the plugin decide whether to render or not
     const plugin = findFileRenderPlugin(basename(rawFileLink), mimeType);
diff --git a/web_src/js/features/heatmap.ts b/web_src/js/features/heatmap.ts
index 7cec82108b..0c13d1c98a 100644
--- a/web_src/js/features/heatmap.ts
+++ b/web_src/js/features/heatmap.ts
@@ -8,7 +8,7 @@ export function initHeatmap() {
 
   try {
     const heatmap: Record<string, number> = {};
-    for (const {contributions, timestamp} of JSON.parse(el.getAttribute('data-heatmap-data'))) {
+    for (const {contributions, timestamp} of JSON.parse(el.getAttribute('data-heatmap-data')!)) {
       // Convert to user timezone and sum contributions by date
       const dateStr = new Date(timestamp * 1000).toDateString();
       heatmap[dateStr] = (heatmap[dateStr] || 0) + contributions;
diff --git a/web_src/js/features/imagediff.ts b/web_src/js/features/imagediff.ts
index 20682f74d9..4ace1ca2ad 100644
--- a/web_src/js/features/imagediff.ts
+++ b/web_src/js/features/imagediff.ts
@@ -78,7 +78,7 @@ class ImageDiff {
     fomanticQuery(containerEl).find('.ui.menu.tabular .item').tab();
 
     // the container may be hidden by "viewed" checkbox, so use the parent's width for reference
-    this.diffContainerWidth = Math.max(containerEl.closest('.diff-file-box').clientWidth - 300, 100);
+    this.diffContainerWidth = Math.max(containerEl.closest('.diff-file-box')!.clientWidth - 300, 100);
 
     const imageInfos = [{
       path: containerEl.getAttribute('data-path-after'),
@@ -94,20 +94,20 @@ class ImageDiff {
 
     await Promise.all(imageInfos.map(async (info) => {
       const [success] = await Promise.all(Array.from(info.images, (img) => {
-        return loadElem(img, info.path);
+        return loadElem(img, info.path!);
       }));
       // only the first images is associated with boundsInfo
       if (!success && info.boundsInfo) info.boundsInfo.textContent = '(image error)';
       if (info.mime === 'image/svg+xml') {
-        const resp = await GET(info.path);
+        const resp = await GET(info.path!);
         const text = await resp.text();
-        const bounds = getDefaultSvgBoundsIfUndefined(text, info.path);
+        const bounds = getDefaultSvgBoundsIfUndefined(text, info.path!);
         if (bounds) {
           for (const el of info.images) {
             el.setAttribute('width', String(bounds.width));
             el.setAttribute('height', String(bounds.height));
           }
-          hideElem(info.boundsInfo);
+          hideElem(info.boundsInfo!);
         }
       }
     }));
@@ -213,7 +213,7 @@ class ImageDiff {
       swipe.style.height = `${sizes.maxSize.height * factor + 30}px`;
     }
 
-    this.containerEl.querySelector('.swipe-bar').addEventListener('mousedown', (e) => {
+    this.containerEl.querySelector('.swipe-bar')!.addEventListener('mousedown', (e) => {
       e.preventDefault();
       this.initSwipeEventListeners(e.currentTarget as HTMLElement);
     });
@@ -227,7 +227,7 @@ class ImageDiff {
       const rect = swipeFrame.getBoundingClientRect();
       const value = Math.max(0, Math.min(e.clientX - rect.left, width));
       swipeBar.style.left = `${value}px`;
-      this.containerEl.querySelector<HTMLElement>('.swipe-container').style.width = `${swipeFrame.clientWidth - value}px`;
+      this.containerEl.querySelector<HTMLElement>('.swipe-container')!.style.width = `${swipeFrame.clientWidth - value}px`;
     };
     const removeEventListeners = () => {
       document.removeEventListener('mousemove', onSwipeMouseMove);
@@ -266,7 +266,7 @@ class ImageDiff {
       overlayFrame.style.height = `${sizes.maxSize.height * factor + 2}px`;
     }
 
-    const rangeInput = this.containerEl.querySelector<HTMLInputElement>('input[type="range"]');
+    const rangeInput = this.containerEl.querySelector<HTMLInputElement>('input[type="range"]')!;
 
     function updateOpacity() {
       if (sizes.imageAfter) {
diff --git a/web_src/js/features/install.ts b/web_src/js/features/install.ts
index ca4bcce881..c00fe3c03d 100644
--- a/web_src/js/features/install.ts
+++ b/web_src/js/features/install.ts
@@ -23,12 +23,12 @@ function initPreInstall() {
     mssql: '127.0.0.1:1433',
   };
 
-  const dbHost = document.querySelector<HTMLInputElement>('#db_host');
-  const dbUser = document.querySelector<HTMLInputElement>('#db_user');
-  const dbName = document.querySelector<HTMLInputElement>('#db_name');
+  const dbHost = document.querySelector<HTMLInputElement>('#db_host')!;
+  const dbUser = document.querySelector<HTMLInputElement>('#db_user')!;
+  const dbName = document.querySelector<HTMLInputElement>('#db_name')!;
 
   // Database type change detection.
-  document.querySelector<HTMLInputElement>('#db_type').addEventListener('change', function () {
+  document.querySelector<HTMLInputElement>('#db_type')!.addEventListener('change', function () {
     const dbType = this.value;
     hideElem('div[data-db-setting-for]');
     showElem(`div[data-db-setting-for=${dbType}]`);
@@ -47,58 +47,58 @@ function initPreInstall() {
       }
     } // else: for SQLite3, the default path is always prepared by backend code (setting)
   });
-  document.querySelector('#db_type').dispatchEvent(new Event('change'));
+  document.querySelector('#db_type')!.dispatchEvent(new Event('change'));
 
-  const appUrl = document.querySelector<HTMLInputElement>('#app_url');
+  const appUrl = document.querySelector<HTMLInputElement>('#app_url')!;
   if (appUrl.value.includes('://localhost')) {
     appUrl.value = window.location.href;
   }
 
-  const domain = document.querySelector<HTMLInputElement>('#domain');
+  const domain = document.querySelector<HTMLInputElement>('#domain')!;
   if (domain.value.trim() === 'localhost') {
     domain.value = window.location.hostname;
   }
 
   // TODO: better handling of exclusive relations.
-  document.querySelector<HTMLInputElement>('#offline-mode input').addEventListener('change', function () {
+  document.querySelector<HTMLInputElement>('#offline-mode input')!.addEventListener('change', function () {
     if (this.checked) {
-      document.querySelector<HTMLInputElement>('#disable-gravatar input').checked = true;
-      document.querySelector<HTMLInputElement>('#federated-avatar-lookup input').checked = false;
+      document.querySelector<HTMLInputElement>('#disable-gravatar input')!.checked = true;
+      document.querySelector<HTMLInputElement>('#federated-avatar-lookup input')!.checked = false;
     }
   });
-  document.querySelector<HTMLInputElement>('#disable-gravatar input').addEventListener('change', function () {
+  document.querySelector<HTMLInputElement>('#disable-gravatar input')!.addEventListener('change', function () {
     if (this.checked) {
-      document.querySelector<HTMLInputElement>('#federated-avatar-lookup input').checked = false;
+      document.querySelector<HTMLInputElement>('#federated-avatar-lookup input')!.checked = false;
     } else {
-      document.querySelector<HTMLInputElement>('#offline-mode input').checked = false;
+      document.querySelector<HTMLInputElement>('#offline-mode input')!.checked = false;
     }
   });
-  document.querySelector<HTMLInputElement>('#federated-avatar-lookup input').addEventListener('change', function () {
+  document.querySelector<HTMLInputElement>('#federated-avatar-lookup input')!.addEventListener('change', function () {
     if (this.checked) {
-      document.querySelector<HTMLInputElement>('#disable-gravatar input').checked = false;
-      document.querySelector<HTMLInputElement>('#offline-mode input').checked = false;
+      document.querySelector<HTMLInputElement>('#disable-gravatar input')!.checked = false;
+      document.querySelector<HTMLInputElement>('#offline-mode input')!.checked = false;
     }
   });
-  document.querySelector<HTMLInputElement>('#enable-openid-signin input').addEventListener('change', function () {
+  document.querySelector<HTMLInputElement>('#enable-openid-signin input')!.addEventListener('change', function () {
     if (this.checked) {
-      if (!document.querySelector<HTMLInputElement>('#disable-registration input').checked) {
-        document.querySelector<HTMLInputElement>('#enable-openid-signup input').checked = true;
+      if (!document.querySelector<HTMLInputElement>('#disable-registration input')!.checked) {
+        document.querySelector<HTMLInputElement>('#enable-openid-signup input')!.checked = true;
       }
     } else {
-      document.querySelector<HTMLInputElement>('#enable-openid-signup input').checked = false;
+      document.querySelector<HTMLInputElement>('#enable-openid-signup input')!.checked = false;
     }
   });
-  document.querySelector<HTMLInputElement>('#disable-registration input').addEventListener('change', function () {
+  document.querySelector<HTMLInputElement>('#disable-registration input')!.addEventListener('change', function () {
     if (this.checked) {
-      document.querySelector<HTMLInputElement>('#enable-captcha input').checked = false;
-      document.querySelector<HTMLInputElement>('#enable-openid-signup input').checked = false;
+      document.querySelector<HTMLInputElement>('#enable-captcha input')!.checked = false;
+      document.querySelector<HTMLInputElement>('#enable-openid-signup input')!.checked = false;
     } else {
-      document.querySelector<HTMLInputElement>('#enable-openid-signup input').checked = true;
+      document.querySelector<HTMLInputElement>('#enable-openid-signup input')!.checked = true;
     }
   });
-  document.querySelector<HTMLInputElement>('#enable-captcha input').addEventListener('change', function () {
+  document.querySelector<HTMLInputElement>('#enable-captcha input')!.addEventListener('change', function () {
     if (this.checked) {
-      document.querySelector<HTMLInputElement>('#disable-registration input').checked = false;
+      document.querySelector<HTMLInputElement>('#disable-registration input')!.checked = false;
     }
   });
 }
@@ -107,8 +107,8 @@ function initPostInstall() {
   const el = document.querySelector('#goto-after-install');
   if (!el) return;
 
-  const targetUrl = el.getAttribute('href');
-  let tid = setInterval(async () => {
+  const targetUrl = el.getAttribute('href')!;
+  let tid: ReturnType<typeof setInterval> | null = setInterval(async () => {
     try {
       const resp = await GET(targetUrl);
       if (tid && resp.status === 200) {
diff --git a/web_src/js/features/notification.ts b/web_src/js/features/notification.ts
index 4a1aa3ede9..ae318e6c78 100644
--- a/web_src/js/features/notification.ts
+++ b/web_src/js/features/notification.ts
@@ -90,7 +90,7 @@ export function initNotificationCount() {
 }
 
 function getCurrentCount() {
-  return Number(document.querySelector('.notification_count').textContent ?? '0');
+  return Number(document.querySelector('.notification_count')!.textContent ?? '0');
 }
 
 async function updateNotificationCountWithCallback(callback: (timeout: number, newCount: number) => void, timeout: number, lastCount: number) {
@@ -131,9 +131,9 @@ async function updateNotificationTable() {
 
       const data = await response.text();
       const el = createElementFromHTML(data);
-      if (parseInt(el.getAttribute('data-sequence-number')) === notificationSequenceNumber) {
+      if (parseInt(el.getAttribute('data-sequence-number')!) === notificationSequenceNumber) {
         notificationDiv.outerHTML = data;
-        notificationDiv = document.querySelector('#notification_div');
+        notificationDiv = document.querySelector('#notification_div')!;
         window.htmx.process(notificationDiv); // when using htmx, we must always remember to process the new content changed by us
       }
     } catch (error) {
diff --git a/web_src/js/features/oauth2-settings.ts b/web_src/js/features/oauth2-settings.ts
index 40424babb8..8d00ae3c17 100644
--- a/web_src/js/features/oauth2-settings.ts
+++ b/web_src/js/features/oauth2-settings.ts
@@ -1,9 +1,9 @@
-import type {DOMEvent} from '../utils/dom.ts';
-
 export function initOAuth2SettingsDisableCheckbox() {
   for (const el of document.querySelectorAll<HTMLInputElement>('.disable-setting')) {
-    el.addEventListener('change', (e: DOMEvent<Event, HTMLInputElement>) => {
-      document.querySelector(e.target.getAttribute('data-target')).classList.toggle('disabled', e.target.checked);
+    el.addEventListener('change', (e) => {
+      const target = e.target as HTMLInputElement;
+      const dataTarget = target.getAttribute('data-target')!;
+      document.querySelector(dataTarget)!.classList.toggle('disabled', target.checked);
     });
   }
 }
diff --git a/web_src/js/features/pull-view-file.ts b/web_src/js/features/pull-view-file.ts
index e563c13ef5..7cf6eceda4 100644
--- a/web_src/js/features/pull-view-file.ts
+++ b/web_src/js/features/pull-view-file.ts
@@ -14,8 +14,8 @@ const collapseFilesBtnSelector = '#collapse-files-btn';
 function refreshViewedFilesSummary() {
   const viewedFilesProgress = document.querySelector('#viewed-files-summary');
   viewedFilesProgress?.setAttribute('value', prReview.numberOfViewedFiles);
-  const summaryLabel = document.querySelector('#viewed-files-summary-label');
-  if (summaryLabel) summaryLabel.innerHTML = summaryLabel.getAttribute('data-text-changed-template')
+  const summaryLabel = document.querySelector('#viewed-files-summary-label')!;
+  if (summaryLabel) summaryLabel.innerHTML = summaryLabel.getAttribute('data-text-changed-template')!
     .replace('%[1]d', prReview.numberOfViewedFiles)
     .replace('%[2]d', prReview.numberOfFiles);
 }
@@ -30,7 +30,7 @@ export function initViewedCheckboxListenerFor() {
 
     // The checkbox consists of a div containing the real checkbox with its label and the CSRF token,
     // hence the actual checkbox first has to be found
-    const checkbox = form.querySelector<HTMLInputElement>('input[type=checkbox]');
+    const checkbox = form.querySelector<HTMLInputElement>('input[type=checkbox]')!;
     checkbox.addEventListener('input', function() {
       // Mark the file as viewed visually - will especially change the background
       if (this.checked) {
@@ -45,10 +45,10 @@ export function initViewedCheckboxListenerFor() {
 
       // Update viewed-files summary and remove "has changed" label if present
       refreshViewedFilesSummary();
-      const hasChangedLabel = form.parentNode.querySelector('.changed-since-last-review');
+      const hasChangedLabel = form.parentNode!.querySelector('.changed-since-last-review');
       hasChangedLabel?.remove();
 
-      const fileName = checkbox.getAttribute('name');
+      const fileName = checkbox.getAttribute('name')!;
 
       // check if the file is in our diffTreeStore and if we find it -> change the IsViewed status
       diffTreeStoreSetViewed(diffTreeStore(), fileName, this.checked);
@@ -59,11 +59,11 @@ export function initViewedCheckboxListenerFor() {
       const data: Record<string, any> = {files};
       const headCommitSHA = form.getAttribute('data-headcommit');
       if (headCommitSHA) data.headCommitSHA = headCommitSHA;
-      POST(form.getAttribute('data-link'), {data});
+      POST(form.getAttribute('data-link')!, {data});
 
       // Fold the file accordingly
-      const parentBox = form.closest('.diff-file-header');
-      setFileFolding(parentBox.closest('.file-content'), parentBox.querySelector('.fold-file'), this.checked);
+      const parentBox = form.closest('.diff-file-header')!;
+      setFileFolding(parentBox.closest('.file-content')!, parentBox.querySelector('.fold-file')!, this.checked);
     });
   }
 }
@@ -72,14 +72,14 @@ export function initExpandAndCollapseFilesButton() {
   // expand btn
   document.querySelector(expandFilesBtnSelector)?.addEventListener('click', () => {
     for (const box of document.querySelectorAll<HTMLElement>('.file-content[data-folded="true"]')) {
-      setFileFolding(box, box.querySelector('.fold-file'), false);
+      setFileFolding(box, box.querySelector('.fold-file')!, false);
     }
   });
   // collapse btn, need to exclude the div of “show more”
   document.querySelector(collapseFilesBtnSelector)?.addEventListener('click', () => {
     for (const box of document.querySelectorAll<HTMLElement>('.file-content:not([data-folded="true"])')) {
       if (box.getAttribute('id') === 'diff-incomplete') continue;
-      setFileFolding(box, box.querySelector('.fold-file'), true);
+      setFileFolding(box, box.querySelector('.fold-file')!, true);
     }
   });
 }
diff --git a/web_src/js/features/repo-branch.ts b/web_src/js/features/repo-branch.ts
index 0c1077748b..4657425f36 100644
--- a/web_src/js/features/repo-branch.ts
+++ b/web_src/js/features/repo-branch.ts
@@ -16,9 +16,9 @@ function initRepoCreateBranchButton() {
       modalForm.action = `${modalForm.getAttribute('data-base-action')}${el.getAttribute('data-branch-from-urlcomponent')}`;
 
       const fromSpanName = el.getAttribute('data-modal-from-span') || '#modal-create-branch-from-span';
-      document.querySelector(fromSpanName).textContent = el.getAttribute('data-branch-from');
+      document.querySelector(fromSpanName)!.textContent = el.getAttribute('data-branch-from');
 
-      fomanticQuery(el.getAttribute('data-modal')).modal('show');
+      fomanticQuery(el.getAttribute('data-modal')!).modal('show');
     });
   }
 }
@@ -26,17 +26,17 @@ function initRepoCreateBranchButton() {
 function initRepoRenameBranchButton() {
   for (const el of document.querySelectorAll('.show-rename-branch-modal')) {
     el.addEventListener('click', () => {
-      const target = el.getAttribute('data-modal');
-      const modal = document.querySelector(target);
-      const oldBranchName = el.getAttribute('data-old-branch-name');
-      modal.querySelector<HTMLInputElement>('input[name=from]').value = oldBranchName;
+      const target = el.getAttribute('data-modal')!;
+      const modal = document.querySelector(target)!;
+      const oldBranchName = el.getAttribute('data-old-branch-name')!;
+      modal.querySelector<HTMLInputElement>('input[name=from]')!.value = oldBranchName;
 
       // display the warning that the branch which is chosen is the default branch
-      const warn = modal.querySelector('.default-branch-warning');
+      const warn = modal.querySelector('.default-branch-warning')!;
       toggleElem(warn, el.getAttribute('data-is-default-branch') === 'true');
 
-      const text = modal.querySelector('[data-rename-branch-to]');
-      text.textContent = text.getAttribute('data-rename-branch-to').replace('%s', oldBranchName);
+      const text = modal.querySelector('[data-rename-branch-to]')!;
+      text.textContent = text.getAttribute('data-rename-branch-to')!.replace('%s', oldBranchName);
     });
   }
 }
diff --git a/web_src/js/features/repo-code.ts b/web_src/js/features/repo-code.ts
index bf7fd762b0..c2dc86cea5 100644
--- a/web_src/js/features/repo-code.ts
+++ b/web_src/js/features/repo-code.ts
@@ -5,14 +5,14 @@ import {addDelegatedEventListener} from '../utils/dom.ts';
 
 function changeHash(hash: string) {
   if (window.history.pushState) {
-    window.history.pushState(null, null, hash);
+    window.history.pushState(null, '', hash);
   } else {
     window.location.hash = hash;
   }
 }
 
 // it selects the code lines defined by range: `L1-L3` (3 lines) or `L2` (singe line)
-function selectRange(range: string): Element {
+function selectRange(range: string): Element | null {
   for (const el of document.querySelectorAll('.code-view tr.active')) el.classList.remove('active');
   const elLineNums = document.querySelectorAll(`.code-view td.lines-num span[data-line-number]`);
 
@@ -23,14 +23,14 @@ function selectRange(range: string): Element {
   const updateIssueHref = function (anchor: string) {
     if (!refInNewIssue) return;
     const urlIssueNew = refInNewIssue.getAttribute('data-url-issue-new');
-    const urlParamBodyLink = refInNewIssue.getAttribute('data-url-param-body-link');
+    const urlParamBodyLink = refInNewIssue.getAttribute('data-url-param-body-link')!;
     const issueContent = `${toAbsoluteUrl(urlParamBodyLink)}#${anchor}`; // the default content for issue body
     refInNewIssue.setAttribute('href', `${urlIssueNew}?body=${encodeURIComponent(issueContent)}`);
   };
 
   const updateViewGitBlameFragment = function (anchor: string) {
     if (!viewGitBlame) return;
-    let href = viewGitBlame.getAttribute('href');
+    let href = viewGitBlame.getAttribute('href')!;
     href = `${href.replace(/#L\d+$|#L\d+-L\d+$/, '')}`;
     if (anchor.length !== 0) {
       href = `${href}#${anchor}`;
@@ -40,7 +40,7 @@ function selectRange(range: string): Element {
 
   const updateCopyPermalinkUrl = function (anchor: string) {
     if (!copyPermalink) return;
-    let link = copyPermalink.getAttribute('data-url');
+    let link = copyPermalink.getAttribute('data-url')!;
     link = `${link.replace(/#L\d+$|#L\d+-L\d+$/, '')}#${anchor}`;
     copyPermalink.setAttribute('data-clipboard-text', link);
     copyPermalink.setAttribute('data-clipboard-text-type', 'url');
@@ -63,7 +63,7 @@ function selectRange(range: string): Element {
 
   const first = elLineNums[startLineNum - 1] ?? null;
   for (let i = startLineNum - 1; i <= stopLineNum - 1 && i < elLineNums.length; i++) {
-    elLineNums[i].closest('tr').classList.add('active');
+    elLineNums[i].closest('tr')!.classList.add('active');
   }
   changeHash(`#${range}`);
   updateIssueHref(range);
@@ -85,14 +85,14 @@ function showLineButton() {
   const tr = document.querySelector('.code-view tr.active');
   if (!tr) return;
 
-  const td = tr.querySelector('td.lines-num');
+  const td = tr.querySelector('td.lines-num')!;
   const btn = document.createElement('button');
   btn.classList.add('code-line-button', 'ui', 'basic', 'button');
   btn.innerHTML = svg('octicon-kebab-horizontal');
   td.prepend(btn);
 
   // put a copy of the menu back into DOM for the next click
-  btn.closest('.code-view').append(menu.cloneNode(true));
+  btn.closest('.code-view')!.append(menu.cloneNode(true));
 
   createTippy(btn, {
     theme: 'menu',
@@ -117,16 +117,16 @@ export function initRepoCodeView() {
   if (!document.querySelector('.repo-view-container .file-view')) return;
 
   // "file code view" and "blame" pages need this "line number button" feature
-  let selRangeStart: string;
+  let selRangeStart: string | undefined;
   addDelegatedEventListener(document, 'click', '.code-view .lines-num span', (el: HTMLElement, e: KeyboardEvent) => {
     if (!selRangeStart || !e.shiftKey) {
-      selRangeStart = el.getAttribute('id');
+      selRangeStart = el.getAttribute('id')!;
       selectRange(selRangeStart);
     } else {
       const selRangeStop = el.getAttribute('id');
       selectRange(`${selRangeStart}-${selRangeStop}`);
     }
-    window.getSelection().removeAllRanges();
+    window.getSelection()!.removeAllRanges();
     showLineButton();
   });
 
diff --git a/web_src/js/features/repo-commit.ts b/web_src/js/features/repo-commit.ts
index 98ec2328ec..16f3899374 100644
--- a/web_src/js/features/repo-commit.ts
+++ b/web_src/js/features/repo-commit.ts
@@ -6,14 +6,14 @@ export function initRepoEllipsisButton() {
   registerGlobalEventFunc('click', 'onRepoEllipsisButtonClick', async (el: HTMLInputElement, e: Event) => {
     e.preventDefault();
     const expanded = el.getAttribute('aria-expanded') === 'true';
-    toggleElem(el.parentElement.querySelector('.commit-body'));
+    toggleElem(el.parentElement!.querySelector('.commit-body')!);
     el.setAttribute('aria-expanded', String(!expanded));
   });
 }
 
 export function initCommitStatuses() {
   registerGlobalInitFunc('initCommitStatuses', (el: HTMLElement) => {
-    const nextEl = el.nextElementSibling;
+    const nextEl = el.nextElementSibling!;
     if (!nextEl.matches('.tippy-target')) throw new Error('Expected next element to be a tippy target');
     createTippy(el, {
       content: nextEl,
diff --git a/web_src/js/features/repo-common.ts b/web_src/js/features/repo-common.ts
index ebb6881c67..ac753805d3 100644
--- a/web_src/js/features/repo-common.ts
+++ b/web_src/js/features/repo-common.ts
@@ -1,4 +1,4 @@
-import {queryElems, type DOMEvent} from '../utils/dom.ts';
+import {queryElems} from '../utils/dom.ts';
 import {POST} from '../modules/fetch.ts';
 import {showErrorToast} from '../modules/toast.ts';
 import {sleep} from '../utils.ts';
@@ -7,10 +7,10 @@ import {createApp} from 'vue';
 import {toOriginUrl} from '../utils/url.ts';
 import {createTippy} from '../modules/tippy.ts';
 
-async function onDownloadArchive(e: DOMEvent<MouseEvent>) {
+async function onDownloadArchive(e: Event) {
   e.preventDefault();
   // there are many places using the "archive-link", eg: the dropdown on the repo code page, the release list
-  const el = e.target.closest<HTMLAnchorElement>('a.archive-link[href]');
+  const el = (e.target as HTMLElement).closest<HTMLAnchorElement>('a.archive-link[href]')!;
   const targetLoading = el.closest('.ui.dropdown') ?? el;
   targetLoading.classList.add('is-loading', 'loading-icon-2px');
   try {
@@ -51,13 +51,13 @@ export function substituteRepoOpenWithUrl(tmpl: string, url: string): string {
 }
 
 function initCloneSchemeUrlSelection(parent: Element) {
-  const elCloneUrlInput = parent.querySelector<HTMLInputElement>('.repo-clone-url');
+  const elCloneUrlInput = parent.querySelector<HTMLInputElement>('.repo-clone-url')!;
 
   const tabHttps = parent.querySelector('.repo-clone-https');
   const tabSsh = parent.querySelector('.repo-clone-ssh');
   const tabTea = parent.querySelector('.repo-clone-tea');
   const updateClonePanelUi = function() {
-    let scheme = localStorage.getItem('repo-clone-protocol');
+    let scheme = localStorage.getItem('repo-clone-protocol')!;
     if (!['https', 'ssh', 'tea'].includes(scheme)) {
       scheme = 'https';
     }
@@ -87,7 +87,7 @@ function initCloneSchemeUrlSelection(parent: Element) {
       tabTea.classList.toggle('active', isTea);
     }
 
-    let tab: Element;
+    let tab: Element | null = null;
     if (isHttps) {
       tab = tabHttps;
     } else if (isSsh) {
@@ -97,7 +97,7 @@ function initCloneSchemeUrlSelection(parent: Element) {
     }
 
     if (!tab) return;
-    const link = toOriginUrl(tab.getAttribute('data-link'));
+    const link = toOriginUrl(tab.getAttribute('data-link')!);
 
     for (const el of document.querySelectorAll('.js-clone-url')) {
       if (el.nodeName === 'INPUT') {
@@ -107,7 +107,7 @@ function initCloneSchemeUrlSelection(parent: Element) {
       }
     }
     for (const el of parent.querySelectorAll<HTMLAnchorElement>('.js-clone-url-editor')) {
-      el.href = substituteRepoOpenWithUrl(el.getAttribute('data-href-template'), link);
+      el.href = substituteRepoOpenWithUrl(el.getAttribute('data-href-template')!, link);
     }
   };
 
@@ -131,7 +131,7 @@ function initCloneSchemeUrlSelection(parent: Element) {
 }
 
 function initClonePanelButton(btn: HTMLButtonElement) {
-  const elPanel = btn.nextElementSibling;
+  const elPanel = btn.nextElementSibling!;
   // "init" must be before the "createTippy" otherwise the "tippy-target" will be removed from the document
   initCloneSchemeUrlSelection(elPanel);
   createTippy(btn, {
diff --git a/web_src/js/features/repo-diff-commit.ts b/web_src/js/features/repo-diff-commit.ts
index b270fb8568..ac5d7baca6 100644
--- a/web_src/js/features/repo-diff-commit.ts
+++ b/web_src/js/features/repo-diff-commit.ts
@@ -4,7 +4,7 @@ import {GET} from '../modules/fetch.ts';
 async function loadBranchesAndTags(area: Element, loadingButton: Element) {
   loadingButton.classList.add('disabled');
   try {
-    const res = await GET(loadingButton.getAttribute('data-fetch-url'));
+    const res = await GET(loadingButton.getAttribute('data-fetch-url')!);
     const data = await res.json();
     hideElem(loadingButton);
     addTags(area, data.tags);
@@ -16,8 +16,8 @@ async function loadBranchesAndTags(area: Element, loadingButton: Element) {
 }
 
 function addTags(area: Element, tags: Array<Record<string, any>>) {
-  const tagArea = area.querySelector('.tag-area');
-  toggleElem(tagArea.parentElement, tags.length > 0);
+  const tagArea = area.querySelector('.tag-area')!;
+  toggleElem(tagArea.parentElement!, tags.length > 0);
   for (const tag of tags) {
     addLink(tagArea, tag.web_link, tag.name);
   }
@@ -25,15 +25,15 @@ function addTags(area: Element, tags: Array<Record<string, any>>) {
 
 function addBranches(area: Element, branches: Array<Record<string, any>>, defaultBranch: string) {
   const defaultBranchTooltip = area.getAttribute('data-text-default-branch-tooltip');
-  const branchArea = area.querySelector('.branch-area');
-  toggleElem(branchArea.parentElement, branches.length > 0);
+  const branchArea = area.querySelector('.branch-area')!;
+  toggleElem(branchArea.parentElement!, branches.length > 0);
   for (const branch of branches) {
     const tooltip = defaultBranch === branch.name ? defaultBranchTooltip : null;
     addLink(branchArea, branch.web_link, branch.name, tooltip);
   }
 }
 
-function addLink(parent: Element, href: string, text: string, tooltip?: string) {
+function addLink(parent: Element, href: string, text: string, tooltip: string | null = null) {
   const link = document.createElement('a');
   link.classList.add('muted', 'tw-px-1');
   link.href = href;
@@ -47,7 +47,7 @@ function addLink(parent: Element, href: string, text: string, tooltip?: string)
 
 export function initRepoDiffCommitBranchesAndTags() {
   for (const area of document.querySelectorAll('.branch-and-tag-area')) {
-    const btn = area.querySelector('.load-branches-and-tags');
+    const btn = area.querySelector('.load-branches-and-tags')!;
     btn.addEventListener('click', () => loadBranchesAndTags(area, btn));
   }
 }
diff --git a/web_src/js/features/repo-diff.ts b/web_src/js/features/repo-diff.ts
index 6f5cb2f63b..20f27f31bc 100644
--- a/web_src/js/features/repo-diff.ts
+++ b/web_src/js/features/repo-diff.ts
@@ -18,7 +18,7 @@ function initRepoDiffFileBox(el: HTMLElement) {
     queryElemSiblings(btn, '.file-view-toggle', (el) => el.classList.remove('active'));
     btn.classList.add('active');
 
-    const target = document.querySelector(btn.getAttribute('data-toggle-selector'));
+    const target = document.querySelector(btn.getAttribute('data-toggle-selector')!);
     if (!target) throw new Error('Target element not found');
 
     hideElem(queryElemSiblings(target));
@@ -31,7 +31,7 @@ function initRepoDiffConversationForm() {
   // This listener is for "reply form" only, it should clearly distinguish different forms in the future.
   addDelegatedEventListener<HTMLFormElement, SubmitEvent>(document, 'submit', '.conversation-holder form', async (form, e) => {
     e.preventDefault();
-    const textArea = form.querySelector<HTMLTextAreaElement>('textarea');
+    const textArea = form.querySelector<HTMLTextAreaElement>('textarea')!;
     if (!validateTextareaNonEmpty(textArea)) return;
     if (form.classList.contains('is-loading')) return;
 
@@ -49,14 +49,15 @@ function initRepoDiffConversationForm() {
       // on the diff page, the form is inside a "tr" and need to get the line-type ahead
       // but on the conversation page, there is no parent "tr"
       const trLineType = form.closest('tr')?.getAttribute('data-line-type');
-      const response = await POST(form.getAttribute('action'), {data: formData});
+      const response = await POST(form.getAttribute('action')!, {data: formData});
       const newConversationHolder = createElementFromHTML(await response.text());
       const path = newConversationHolder.getAttribute('data-path');
       const side = newConversationHolder.getAttribute('data-side');
       const idx = newConversationHolder.getAttribute('data-idx');
 
-      form.closest('.conversation-holder').replaceWith(newConversationHolder);
-      form = null; // prevent further usage of the form because it should have been replaced
+      form.closest('.conversation-holder')!.replaceWith(newConversationHolder);
+      // @ts-expect-error -- prevent further usage of the form because it should have been replaced
+      form = null;
 
       if (trLineType) {
         // if there is a line-type for the "tr", it means the form is on the diff page
@@ -74,10 +75,10 @@ function initRepoDiffConversationForm() {
 
       // the default behavior is to add a pending review, so if no submitter, it also means "pending_review"
       if (!submitter || submitter?.matches('button[name="pending_review"]')) {
-        const reviewBox = document.querySelector('#review-box');
+        const reviewBox = document.querySelector('#review-box')!;
         const counter = reviewBox?.querySelector('.review-comments-counter');
         if (!counter) return;
-        const num = parseInt(counter.getAttribute('data-pending-comment-number')) + 1 || 1;
+        const num = parseInt(counter.getAttribute('data-pending-comment-number')!) + 1 || 1;
         counter.setAttribute('data-pending-comment-number', String(num));
         counter.textContent = String(num);
         animateOnce(reviewBox, 'pulse-1p5-200');
@@ -92,10 +93,10 @@ function initRepoDiffConversationForm() {
 
   addDelegatedEventListener(document, 'click', '.resolve-conversation', async (el, e) => {
     e.preventDefault();
-    const comment_id = el.getAttribute('data-comment-id');
-    const origin = el.getAttribute('data-origin');
-    const action = el.getAttribute('data-action');
-    const url = el.getAttribute('data-update-url');
+    const comment_id = el.getAttribute('data-comment-id')!;
+    const origin = el.getAttribute('data-origin')!;
+    const action = el.getAttribute('data-action')!;
+    const url = el.getAttribute('data-update-url')!;
 
     try {
       const response = await POST(url, {data: new URLSearchParams({origin, action, comment_id})});
@@ -119,14 +120,14 @@ function initRepoDiffConversationNav() {
   addDelegatedEventListener(document, 'click', '.previous-conversation, .next-conversation', (el, e) => {
     e.preventDefault();
     const isPrevious = el.matches('.previous-conversation');
-    const elCurConversation = el.closest('.comment-code-cloud');
+    const elCurConversation = el.closest('.comment-code-cloud')!;
     const elAllConversations = document.querySelectorAll('.comment-code-cloud:not(.tw-hidden)');
     const index = Array.from(elAllConversations).indexOf(elCurConversation);
     const previousIndex = index > 0 ? index - 1 : elAllConversations.length - 1;
     const nextIndex = index < elAllConversations.length - 1 ? index + 1 : 0;
     const navIndex = isPrevious ? previousIndex : nextIndex;
     const elNavConversation = elAllConversations[navIndex];
-    const anchor = elNavConversation.querySelector('.comment').id;
+    const anchor = elNavConversation.querySelector('.comment')!.id;
     window.location.href = `#${anchor}`;
   });
 }
@@ -162,15 +163,15 @@ async function loadMoreFiles(btn: Element): Promise<boolean> {
   }
 
   btn.classList.add('disabled');
-  const url = btn.getAttribute('data-href');
+  const url = btn.getAttribute('data-href')!;
   try {
     const response = await GET(url);
     const resp = await response.text();
     const respDoc = parseDom(resp, 'text/html');
-    const respFileBoxes = respDoc.querySelector('#diff-file-boxes');
+    const respFileBoxes = respDoc.querySelector('#diff-file-boxes')!;
     // the response is a full HTML page, we need to extract the relevant contents:
     // * append the newly loaded file list items to the existing list
-    document.querySelector('#diff-incomplete').replaceWith(...Array.from(respFileBoxes.children));
+    document.querySelector('#diff-incomplete')!.replaceWith(...Array.from(respFileBoxes.children));
     onShowMoreFiles();
     return true;
   } catch (error) {
@@ -193,15 +194,15 @@ function initRepoDiffShowMore() {
     if (el.classList.contains('disabled')) return;
 
     el.classList.add('disabled');
-    const url = el.getAttribute('data-href');
+    const url = el.getAttribute('data-href')!;
 
     try {
       const response = await GET(url);
       const resp = await response.text();
       const respDoc = parseDom(resp, 'text/html');
-      const respFileBody = respDoc.querySelector('#diff-file-boxes .diff-file-body .file-body');
+      const respFileBody = respDoc.querySelector('#diff-file-boxes .diff-file-body .file-body')!;
       const respFileBodyChildren = Array.from(respFileBody.children); // respFileBody.children will be empty after replaceWith
-      el.parentElement.replaceWith(...respFileBodyChildren);
+      el.parentElement!.replaceWith(...respFileBodyChildren);
       for (const el of respFileBodyChildren) window.htmx.process(el);
       // FIXME: calling onShowMoreFiles is not quite right here.
       // But since onShowMoreFiles mixes "init diff box" and "init diff body" together,
@@ -287,6 +288,6 @@ export function initRepoDiffView() {
 
   registerGlobalSelectorFunc('#diff-file-boxes .diff-file-box', initRepoDiffFileBox);
   addDelegatedEventListener(document, 'click', '.fold-file', (el) => {
-    invertFileFolding(el.closest('.file-content'), el);
+    invertFileFolding(el.closest('.file-content')!, el);
   });
 }
diff --git a/web_src/js/features/repo-editor.ts b/web_src/js/features/repo-editor.ts
index 0825999edc..93595c385e 100644
--- a/web_src/js/features/repo-editor.ts
+++ b/web_src/js/features/repo-editor.ts
@@ -9,7 +9,7 @@ import {fomanticQuery} from '../modules/fomantic/base.ts';
 import {submitFormFetchAction} from './common-fetch-action.ts';
 
 function initEditPreviewTab(elForm: HTMLFormElement) {
-  const elTabMenu = elForm.querySelector('.repo-editor-menu');
+  const elTabMenu = elForm.querySelector('.repo-editor-menu')!;
   fomanticQuery(elTabMenu.querySelectorAll('.item')).tab();
 
   const elPreviewTab = elTabMenu.querySelector('a[data-tab="preview"]');
@@ -17,15 +17,15 @@ function initEditPreviewTab(elForm: HTMLFormElement) {
   if (!elPreviewTab || !elPreviewPanel) return;
 
   elPreviewTab.addEventListener('click', async () => {
-    const elTreePath = elForm.querySelector<HTMLInputElement>('input#tree_path');
-    const previewUrl = elPreviewTab.getAttribute('data-preview-url');
+    const elTreePath = elForm.querySelector<HTMLInputElement>('input#tree_path')!;
+    const previewUrl = elPreviewTab.getAttribute('data-preview-url')!;
     const previewContextRef = elPreviewTab.getAttribute('data-preview-context-ref');
     let previewContext = `${previewContextRef}/${elTreePath.value}`;
     previewContext = previewContext.substring(0, previewContext.lastIndexOf('/'));
     const formData = new FormData();
     formData.append('mode', 'file');
     formData.append('context', previewContext);
-    formData.append('text', elForm.querySelector<HTMLTextAreaElement>('.tab[data-tab="write"] textarea').value);
+    formData.append('text', elForm.querySelector<HTMLTextAreaElement>('.tab[data-tab="write"] textarea')!.value);
     formData.append('file_path', elTreePath.value);
     const response = await POST(previewUrl, {data: formData});
     const data = await response.text();
@@ -41,16 +41,16 @@ export function initRepoEditor() {
     el.addEventListener('input', () => {
       if (el.value === 'commit-to-new-branch') {
         showElem('.quick-pull-branch-name');
-        document.querySelector<HTMLInputElement>('.quick-pull-branch-name input').required = true;
+        document.querySelector<HTMLInputElement>('.quick-pull-branch-name input')!.required = true;
       } else {
         hideElem('.quick-pull-branch-name');
-        document.querySelector<HTMLInputElement>('.quick-pull-branch-name input').required = false;
+        document.querySelector<HTMLInputElement>('.quick-pull-branch-name input')!.required = false;
       }
-      document.querySelector('#commit-button').textContent = el.getAttribute('data-button-text');
+      document.querySelector('#commit-button')!.textContent = el.getAttribute('data-button-text');
     });
   }
 
-  const filenameInput = document.querySelector<HTMLInputElement>('#file-name');
+  const filenameInput = document.querySelector<HTMLInputElement>('#file-name')!;
   if (!filenameInput) return;
   function joinTreePath() {
     const parts = [];
@@ -61,7 +61,7 @@ export function initRepoEditor() {
     if (filenameInput.value) {
       parts.push(filenameInput.value);
     }
-    document.querySelector<HTMLInputElement>('#tree_path').value = parts.join('/');
+    document.querySelector<HTMLInputElement>('#tree_path')!.value = parts.join('/');
   }
   filenameInput.addEventListener('input', function () {
     const parts = filenameInput.value.split('/');
@@ -76,8 +76,8 @@ export function initRepoEditor() {
         if (trimValue === '..') {
           // remove previous tree path
           if (links.length > 0) {
-            const link = links.pop();
-            const divider = dividers.pop();
+            const link = links.pop()!;
+            const divider = dividers.pop()!;
             link.remove();
             divider.remove();
           }
@@ -104,7 +104,7 @@ export function initRepoEditor() {
       }
     }
     containSpace = containSpace || Array.from(links).some((link) => {
-      const value = link.querySelector('a').textContent;
+      const value = link.querySelector('a')!.textContent;
       return value.trim() !== value;
     });
     containSpace = containSpace || parts[parts.length - 1].trim() !== parts[parts.length - 1];
@@ -115,7 +115,7 @@ export function initRepoEditor() {
         warningDiv.innerHTML = html`<p>File path contains leading or trailing whitespace.</p>`;
         // Add display 'block' because display is set to 'none' in formantic\build\semantic.css
         warningDiv.style.display = 'block';
-        const inputContainer = document.querySelector('.repo-editor-header');
+        const inputContainer = document.querySelector('.repo-editor-header')!;
         inputContainer.insertAdjacentElement('beforebegin', warningDiv);
       }
       showElem(warningDiv);
@@ -132,7 +132,7 @@ export function initRepoEditor() {
       e.preventDefault();
       const lastSection = sections[sections.length - 1];
       const lastDivider = dividers.length ? dividers[dividers.length - 1] : null;
-      const value = lastSection.querySelector('a').textContent;
+      const value = lastSection.querySelector('a')!.textContent;
       filenameInput.value = value + filenameInput.value;
       this.setSelectionRange(value.length, value.length);
       lastDivider?.remove();
@@ -141,7 +141,7 @@ export function initRepoEditor() {
     }
   });
 
-  const elForm = document.querySelector<HTMLFormElement>('.repository.editor .edit.form');
+  const elForm = document.querySelector<HTMLFormElement>('.repository.editor .edit.form')!;
 
   // on the upload page, there is no editor(textarea)
   const editArea = document.querySelector<HTMLTextAreaElement>('.page-content.repository.editor textarea#edit_area');
@@ -149,7 +149,7 @@ export function initRepoEditor() {
 
   // Using events from https://github.com/codedance/jquery.AreYouSure#advanced-usage
   // to enable or disable the commit button
-  const commitButton = document.querySelector<HTMLButtonElement>('#commit-button');
+  const commitButton = document.querySelector<HTMLButtonElement>('#commit-button')!;
   const dirtyFileClass = 'dirty-file';
 
   const syncCommitButtonState = () => {
@@ -184,8 +184,8 @@ export function initRepoEditor() {
       if (!editArea.value) {
         e.preventDefault();
         if (await confirmModal({
-          header: elForm.getAttribute('data-text-empty-confirm-header'),
-          content: elForm.getAttribute('data-text-empty-confirm-content'),
+          header: elForm.getAttribute('data-text-empty-confirm-header')!,
+          content: elForm.getAttribute('data-text-empty-confirm-content')!,
         })) {
           ignoreAreYouSure(elForm);
           submitFormFetchAction(elForm);
diff --git a/web_src/js/features/repo-graph.ts b/web_src/js/features/repo-graph.ts
index ebca6e212a..2177368b9f 100644
--- a/web_src/js/features/repo-graph.ts
+++ b/web_src/js/features/repo-graph.ts
@@ -6,8 +6,8 @@ export function initRepoGraphGit() {
   const graphContainer = document.querySelector<HTMLElement>('#git-graph-container');
   if (!graphContainer) return;
 
-  const elColorMonochrome = document.querySelector<HTMLElement>('#flow-color-monochrome');
-  const elColorColored = document.querySelector<HTMLElement>('#flow-color-colored');
+  const elColorMonochrome = document.querySelector<HTMLElement>('#flow-color-monochrome')!;
+  const elColorColored = document.querySelector<HTMLElement>('#flow-color-colored')!;
   const toggleColorMode = (mode: 'monochrome' | 'colored') => {
     toggleElemClass(graphContainer, 'monochrome', mode === 'monochrome');
     toggleElemClass(graphContainer, 'colored', mode === 'colored');
@@ -31,7 +31,7 @@ export function initRepoGraphGit() {
   elColorMonochrome.addEventListener('click', () => toggleColorMode('monochrome'));
   elColorColored.addEventListener('click', () => toggleColorMode('colored'));
 
-  const elGraphBody = document.querySelector<HTMLElement>('#git-graph-body');
+  const elGraphBody = document.querySelector<HTMLElement>('#git-graph-body')!;
   const url = new URL(window.location.href);
   const params = url.searchParams;
   const loadGitGraph = async () => {
diff --git a/web_src/js/features/repo-home.ts b/web_src/js/features/repo-home.ts
index 04a1288626..8bc7af6195 100644
--- a/web_src/js/features/repo-home.ts
+++ b/web_src/js/features/repo-home.ts
@@ -1,5 +1,5 @@
 import {stripTags} from '../utils.ts';
-import {hideElem, queryElemChildren, showElem, type DOMEvent} from '../utils/dom.ts';
+import {hideElem, queryElemChildren, showElem} from '../utils/dom.ts';
 import {POST} from '../modules/fetch.ts';
 import {showErrorToast, type Toast} from '../modules/toast.ts';
 import {fomanticQuery} from '../modules/fomantic/base.ts';
@@ -10,32 +10,32 @@ export function initRepoTopicBar() {
   const mgrBtn = document.querySelector<HTMLButtonElement>('#manage_topic');
   if (!mgrBtn) return;
 
-  const editDiv = document.querySelector('#topic_edit');
-  const viewDiv = document.querySelector('#repo-topics');
-  const topicDropdown = editDiv.querySelector('.ui.dropdown');
-  let lastErrorToast: Toast;
+  const editDiv = document.querySelector('#topic_edit')!;
+  const viewDiv = document.querySelector('#repo-topics')!;
+  const topicDropdown = editDiv.querySelector('.ui.dropdown')!;
+  let lastErrorToast: Toast | null = null;
 
   mgrBtn.addEventListener('click', () => {
     hideElem([viewDiv, mgrBtn]);
     showElem(editDiv);
-    topicDropdown.querySelector<HTMLInputElement>('input.search').focus();
+    topicDropdown.querySelector<HTMLInputElement>('input.search')!.focus();
   });
 
-  document.querySelector('#cancel_topic_edit').addEventListener('click', () => {
+  document.querySelector('#cancel_topic_edit')!.addEventListener('click', () => {
     lastErrorToast?.hideToast();
     hideElem(editDiv);
     showElem([viewDiv, mgrBtn]);
     mgrBtn.focus();
   });
 
-  document.querySelector<HTMLButtonElement>('#save_topic').addEventListener('click', async (e: DOMEvent<MouseEvent, HTMLButtonElement>) => {
+  document.querySelector<HTMLButtonElement>('#save_topic')!.addEventListener('click', async (e) => {
     lastErrorToast?.hideToast();
-    const topics = editDiv.querySelector<HTMLInputElement>('input[name=topics]').value;
+    const topics = editDiv.querySelector<HTMLInputElement>('input[name=topics]')!.value;
 
     const data = new FormData();
     data.append('topics', topics);
 
-    const response = await POST(e.target.getAttribute('data-link'), {data});
+    const response = await POST((e.target as HTMLElement).getAttribute('data-link')!, {data});
 
     if (response.ok) {
       const responseData = await response.json();
diff --git a/web_src/js/features/repo-issue-content.ts b/web_src/js/features/repo-issue-content.ts
index 056b810be8..14980e9792 100644
--- a/web_src/js/features/repo-issue-content.ts
+++ b/web_src/js/features/repo-issue-content.ts
@@ -27,7 +27,7 @@ function showContentHistoryDetail(issueBaseUrl: string, commentId: string, histo
   <div class="comment-diff-data is-loading"></div>
 </div>`);
   document.body.append(elDetailDialog);
-  const elOptionsDropdown = elDetailDialog.querySelector('.ui.dropdown.dialog-header-options');
+  const elOptionsDropdown = elDetailDialog.querySelector('.ui.dropdown.dialog-header-options')!;
   const $fomanticDialog = fomanticQuery(elDetailDialog);
   const $fomanticDropdownOptions = fomanticQuery(elOptionsDropdown);
   $fomanticDropdownOptions.dropdown({
@@ -74,7 +74,7 @@ function showContentHistoryDetail(issueBaseUrl: string, commentId: string, histo
         const response = await GET(url);
         const resp = await response.json();
 
-        const commentDiffData = elDetailDialog.querySelector('.comment-diff-data');
+        const commentDiffData = elDetailDialog.querySelector('.comment-diff-data')!;
         commentDiffData.classList.remove('is-loading');
         commentDiffData.innerHTML = resp.diffHtml;
         // there is only one option "item[data-option-item=delete]", so the dropdown can be entirely shown/hidden.
@@ -92,7 +92,7 @@ function showContentHistoryDetail(issueBaseUrl: string, commentId: string, histo
 }
 
 function showContentHistoryMenu(issueBaseUrl: string, elCommentItem: Element, commentId: string) {
-  const elHeaderLeft = elCommentItem.querySelector('.comment-header-left');
+  const elHeaderLeft = elCommentItem.querySelector('.comment-header-left')!;
   const menuHtml = `
   <div class="ui dropdown interact-fg content-history-menu" data-comment-id="${commentId}">
     &bull; ${i18nTextEdited}${svg('octicon-triangle-down', 14, 'dropdown icon')}
@@ -103,7 +103,7 @@ function showContentHistoryMenu(issueBaseUrl: string, elCommentItem: Element, co
   elHeaderLeft.querySelector(`.ui.dropdown.content-history-menu`)?.remove(); // remove the old one if exists
   elHeaderLeft.append(createElementFromHTML(menuHtml));
 
-  const elDropdown = elHeaderLeft.querySelector('.ui.dropdown.content-history-menu');
+  const elDropdown = elHeaderLeft.querySelector('.ui.dropdown.content-history-menu')!;
   const $fomanticDropdown = fomanticQuery(elDropdown);
   $fomanticDropdown.dropdown({
     action: 'hide',
diff --git a/web_src/js/features/repo-issue-edit.ts b/web_src/js/features/repo-issue-edit.ts
index 43aee314e0..6bed000886 100644
--- a/web_src/js/features/repo-issue-edit.ts
+++ b/web_src/js/features/repo-issue-edit.ts
@@ -2,20 +2,20 @@ import {handleReply} from './repo-issue.ts';
 import {getComboMarkdownEditor, initComboMarkdownEditor, ComboMarkdownEditor} from './comp/ComboMarkdownEditor.ts';
 import {POST} from '../modules/fetch.ts';
 import {showErrorToast} from '../modules/toast.ts';
-import {hideElem, querySingleVisibleElem, showElem, type DOMEvent} from '../utils/dom.ts';
+import {hideElem, querySingleVisibleElem, showElem} from '../utils/dom.ts';
 import {triggerUploadStateChanged} from './comp/EditorUpload.ts';
 import {convertHtmlToMarkdown} from '../markup/html2markdown.ts';
 import {applyAreYouSure, reinitializeAreYouSure} from '../vendor/jquery.are-you-sure.ts';
 
-async function tryOnEditContent(e: DOMEvent<MouseEvent>) {
-  const clickTarget = e.target.closest('.edit-content');
+async function tryOnEditContent(e: Event) {
+  const clickTarget = (e.target as HTMLElement).closest('.edit-content');
   if (!clickTarget) return;
 
   e.preventDefault();
-  const commentContent = clickTarget.closest('.comment-header').nextElementSibling;
-  const editContentZone = commentContent.querySelector('.edit-content-zone');
-  let renderContent = commentContent.querySelector('.render-content');
-  const rawContent = commentContent.querySelector('.raw-content');
+  const commentContent = clickTarget.closest('.comment-header')!.nextElementSibling!;
+  const editContentZone = commentContent.querySelector('.edit-content-zone')!;
+  let renderContent = commentContent.querySelector('.render-content')!;
+  const rawContent = commentContent.querySelector('.raw-content')!;
 
   let comboMarkdownEditor : ComboMarkdownEditor;
 
@@ -37,14 +37,14 @@ async function tryOnEditContent(e: DOMEvent<MouseEvent>) {
     try {
       const params = new URLSearchParams({
         content: comboMarkdownEditor.value(),
-        context: editContentZone.getAttribute('data-context'),
-        content_version: editContentZone.getAttribute('data-content-version'),
+        context: String(editContentZone.getAttribute('data-context')),
+        content_version: String(editContentZone.getAttribute('data-content-version')),
       });
       for (const file of comboMarkdownEditor.dropzoneGetFiles() ?? []) {
         params.append('files[]', file);
       }
 
-      const response = await POST(editContentZone.getAttribute('data-update-url'), {data: params});
+      const response = await POST(editContentZone.getAttribute('data-update-url')!, {data: params});
       const data = await response.json();
       if (!response.ok) {
         showErrorToast(data?.errorMessage ?? window.config.i18n.error_occurred);
@@ -67,9 +67,9 @@ async function tryOnEditContent(e: DOMEvent<MouseEvent>) {
           commentContent.insertAdjacentHTML('beforeend', data.attachments);
         }
       } else if (data.attachments === '') {
-        commentContent.querySelector('.dropzone-attachments').remove();
+        commentContent.querySelector('.dropzone-attachments')!.remove();
       } else {
-        commentContent.querySelector('.dropzone-attachments').outerHTML = data.attachments;
+        commentContent.querySelector('.dropzone-attachments')!.outerHTML = data.attachments;
       }
       comboMarkdownEditor.dropzoneSubmitReload();
     } catch (error) {
@@ -86,12 +86,12 @@ async function tryOnEditContent(e: DOMEvent<MouseEvent>) {
 
   comboMarkdownEditor = getComboMarkdownEditor(editContentZone.querySelector('.combo-markdown-editor'));
   if (!comboMarkdownEditor) {
-    editContentZone.innerHTML = document.querySelector('#issue-comment-editor-template').innerHTML;
-    const form = editContentZone.querySelector('form');
+    editContentZone.innerHTML = document.querySelector('#issue-comment-editor-template')!.innerHTML;
+    const form = editContentZone.querySelector('form')!;
     applyAreYouSure(form);
-    const saveButton = querySingleVisibleElem<HTMLButtonElement>(editContentZone, '.ui.primary.button');
-    const cancelButton = querySingleVisibleElem<HTMLButtonElement>(editContentZone, '.ui.cancel.button');
-    comboMarkdownEditor = await initComboMarkdownEditor(editContentZone.querySelector('.combo-markdown-editor'));
+    const saveButton = querySingleVisibleElem<HTMLButtonElement>(editContentZone, '.ui.primary.button')!;
+    const cancelButton = querySingleVisibleElem<HTMLButtonElement>(editContentZone, '.ui.cancel.button')!;
+    comboMarkdownEditor = await initComboMarkdownEditor(editContentZone.querySelector('.combo-markdown-editor')!);
     const syncUiState = () => saveButton.disabled = comboMarkdownEditor.isUploading();
     comboMarkdownEditor.container.addEventListener(ComboMarkdownEditor.EventUploadStateChanged, syncUiState);
     cancelButton.addEventListener('click', cancelAndReset);
@@ -109,7 +109,7 @@ async function tryOnEditContent(e: DOMEvent<MouseEvent>) {
 
 function extractSelectedMarkdown(container: HTMLElement) {
   const selection = window.getSelection();
-  if (!selection.rangeCount) return '';
+  if (!selection?.rangeCount) return '';
   const range = selection.getRangeAt(0);
   if (!container.contains(range.commonAncestorContainer)) return '';
 
@@ -127,15 +127,15 @@ async function tryOnQuoteReply(e: Event) {
 
   e.preventDefault();
   const contentToQuoteId = clickTarget.getAttribute('data-target');
-  const targetRawToQuote = document.querySelector<HTMLElement>(`#${contentToQuoteId}.raw-content`);
-  const targetMarkupToQuote = targetRawToQuote.parentElement.querySelector<HTMLElement>('.render-content.markup');
+  const targetRawToQuote = document.querySelector<HTMLElement>(`#${contentToQuoteId}.raw-content`)!;
+  const targetMarkupToQuote = targetRawToQuote.parentElement!.querySelector<HTMLElement>('.render-content.markup')!;
   let contentToQuote = extractSelectedMarkdown(targetMarkupToQuote);
   if (!contentToQuote) contentToQuote = targetRawToQuote.textContent;
   const quotedContent = `${contentToQuote.replace(/^/mg, '> ')}\n\n`;
 
   let editor;
   if (clickTarget.classList.contains('quote-reply-diff')) {
-    const replyBtn = clickTarget.closest('.comment-code-cloud').querySelector<HTMLElement>('button.comment-form-reply');
+    const replyBtn = clickTarget.closest('.comment-code-cloud')!.querySelector<HTMLElement>('button.comment-form-reply')!;
     editor = await handleReply(replyBtn);
   } else {
     // for normal issue/comment page
diff --git a/web_src/js/features/repo-issue-list.ts b/web_src/js/features/repo-issue-list.ts
index 762fbf51bb..1416d0ee70 100644
--- a/web_src/js/features/repo-issue-list.ts
+++ b/web_src/js/features/repo-issue-list.ts
@@ -34,8 +34,8 @@ function initRepoIssueListCheckboxes() {
     toggleElem('#issue-actions', anyChecked);
     // there are two panels but only one select-all checkbox, so move the checkbox to the visible panel
     const panels = document.querySelectorAll<HTMLElement>('#issue-filters, #issue-actions');
-    const visiblePanel = Array.from(panels).find((el) => isElemVisible(el));
-    const toolbarLeft = visiblePanel.querySelector('.issue-list-toolbar-left');
+    const visiblePanel = Array.from(panels).find((el) => isElemVisible(el))!;
+    const toolbarLeft = visiblePanel.querySelector('.issue-list-toolbar-left')!;
     toolbarLeft.prepend(issueSelectAll);
   };
 
@@ -54,12 +54,12 @@ function initRepoIssueListCheckboxes() {
     async (e: MouseEvent) => {
       e.preventDefault();
 
-      const url = el.getAttribute('data-url');
-      let action = el.getAttribute('data-action');
-      let elementId = el.getAttribute('data-element-id');
+      const url = el.getAttribute('data-url')!;
+      let action = el.getAttribute('data-action')!;
+      let elementId = el.getAttribute('data-element-id')!;
       const issueIDList: string[] = [];
       for (const el of document.querySelectorAll('.issue-checkbox:checked')) {
-        issueIDList.push(el.getAttribute('data-issue-id'));
+        issueIDList.push(el.getAttribute('data-issue-id')!);
       }
       const issueIDs = issueIDList.join(',');
       if (!issueIDs) return;
@@ -77,7 +77,7 @@ function initRepoIssueListCheckboxes() {
 
       // for delete
       if (action === 'delete') {
-        const confirmText = el.getAttribute('data-action-delete-confirm');
+        const confirmText = el.getAttribute('data-action-delete-confirm')!;
         if (!await confirmModal({content: confirmText, confirmButtonColor: 'red'})) {
           return;
         }
@@ -95,12 +95,12 @@ function initRepoIssueListCheckboxes() {
 
 function initDropdownUserRemoteSearch(el: Element) {
   let searchUrl = el.getAttribute('data-search-url');
-  const actionJumpUrl = el.getAttribute('data-action-jump-url');
+  const actionJumpUrl = el.getAttribute('data-action-jump-url')!;
   let selectedUsername = el.getAttribute('data-selected-username') || '';
   const $searchDropdown = fomanticQuery(el);
-  const elMenu = el.querySelector('.menu');
-  const elSearchInput = el.querySelector<HTMLInputElement>('.ui.search input');
-  const elItemFromInput = el.querySelector('.menu > .item-from-input');
+  const elMenu = el.querySelector('.menu')!;
+  const elSearchInput = el.querySelector<HTMLInputElement>('.ui.search input')!;
+  const elItemFromInput = el.querySelector('.menu > .item-from-input')!;
 
   $searchDropdown.dropdown('setting', {
     fullTextSearch: true,
@@ -183,21 +183,21 @@ function initPinRemoveButton() {
       const id = Number(el.getAttribute('data-issue-id'));
 
       // Send the unpin request
-      const response = await DELETE(el.getAttribute('data-unpin-url'));
+      const response = await DELETE(el.getAttribute('data-unpin-url')!);
       if (response.ok) {
         // Delete the tooltip
         el._tippy.destroy();
         // Remove the Card
-        el.closest(`div.issue-card[data-issue-id="${id}"]`).remove();
+        el.closest(`div.issue-card[data-issue-id="${id}"]`)!.remove();
       }
     });
   }
 }
 
 async function pinMoveEnd(e: SortableEvent) {
-  const url = e.item.getAttribute('data-move-url');
+  const url = e.item.getAttribute('data-move-url')!;
   const id = Number(e.item.getAttribute('data-issue-id'));
-  await POST(url, {data: {id, position: e.newIndex + 1}});
+  await POST(url, {data: {id, position: e.newIndex! + 1}});
 }
 
 async function initIssuePinSort() {
diff --git a/web_src/js/features/repo-issue-pull.ts b/web_src/js/features/repo-issue-pull.ts
index c415dad08f..91f27305bd 100644
--- a/web_src/js/features/repo-issue-pull.ts
+++ b/web_src/js/features/repo-issue-pull.ts
@@ -8,21 +8,21 @@ function initRepoPullRequestUpdate(el: HTMLElement) {
   const prUpdateButtonContainer = el.querySelector('#update-pr-branch-with-base');
   if (!prUpdateButtonContainer) return;
 
-  const prUpdateButton = prUpdateButtonContainer.querySelector<HTMLButtonElement>(':scope > button');
-  const prUpdateDropdown = prUpdateButtonContainer.querySelector(':scope > .ui.dropdown');
+  const prUpdateButton = prUpdateButtonContainer.querySelector<HTMLButtonElement>(':scope > button')!;
+  const prUpdateDropdown = prUpdateButtonContainer.querySelector(':scope > .ui.dropdown')!;
   prUpdateButton.addEventListener('click', async function (e) {
     e.preventDefault();
     const redirect = this.getAttribute('data-redirect');
     this.classList.add('is-loading');
-    let response: Response;
+    let response: Response | undefined;
     try {
-      response = await POST(this.getAttribute('data-do'));
+      response = await POST(this.getAttribute('data-do')!);
     } catch (error) {
       console.error(error);
     } finally {
       this.classList.remove('is-loading');
     }
-    let data: Record<string, any>;
+    let data: Record<string, any> | undefined;
     try {
       data = await response?.json(); // the response is probably not a JSON
     } catch (error) {
@@ -54,8 +54,8 @@ function initRepoPullRequestUpdate(el: HTMLElement) {
 
 function initRepoPullRequestCommitStatus(el: HTMLElement) {
   for (const btn of el.querySelectorAll('.commit-status-hide-checks')) {
-    const panel = btn.closest('.commit-status-panel');
-    const list = panel.querySelector<HTMLElement>('.commit-status-list');
+    const panel = btn.closest('.commit-status-panel')!;
+    const list = panel.querySelector<HTMLElement>('.commit-status-list')!;
     btn.addEventListener('click', () => {
       list.style.maxHeight = list.style.maxHeight ? '' : '0px'; // toggle
       btn.textContent = btn.getAttribute(list.style.maxHeight ? 'data-show-all' : 'data-hide-all');
@@ -96,7 +96,7 @@ export function initRepoPullMergeBox(el: HTMLElement) {
 
   const reloadingInterval = parseInt(reloadingIntervalValue);
   const pullLink = el.getAttribute('data-pull-link');
-  let timerId: number;
+  let timerId: number | null;
 
   let reloadMergeBox: () => Promise<void>;
   const stopReloading = () => {
diff --git a/web_src/js/features/repo-issue-sidebar-combolist.ts b/web_src/js/features/repo-issue-sidebar-combolist.ts
index f25c0a77c6..aaff3804c7 100644
--- a/web_src/js/features/repo-issue-sidebar-combolist.ts
+++ b/web_src/js/features/repo-issue-sidebar-combolist.ts
@@ -12,7 +12,7 @@ function issueSidebarReloadConfirmDraftComment() {
     // Most users won't feel too sad if they lose a comment with 10 chars, they can re-type these in seconds.
     // But if they have typed more (like 50) chars and the comment is lost, they will be very unhappy.
     if (textarea && textarea.value.trim().length > 10) {
-      textarea.parentElement.scrollIntoView();
+      textarea.parentElement!.scrollIntoView();
       if (!window.confirm('Page will be reloaded, but there are draft comments. Continuing to reload will discard the comments. Continue?')) {
         return;
       }
@@ -34,22 +34,22 @@ export class IssueSidebarComboList {
 
   constructor(container: HTMLElement) {
     this.container = container;
-    this.updateUrl = container.getAttribute('data-update-url');
-    this.updateAlgo = container.getAttribute('data-update-algo');
-    this.selectionMode = container.getAttribute('data-selection-mode');
+    this.updateUrl = container.getAttribute('data-update-url')!;
+    this.updateAlgo = container.getAttribute('data-update-algo')!;
+    this.selectionMode = container.getAttribute('data-selection-mode')!;
     if (!['single', 'multiple'].includes(this.selectionMode)) throw new Error(`Invalid data-update-on: ${this.selectionMode}`);
     if (!['diff', 'all'].includes(this.updateAlgo)) throw new Error(`Invalid data-update-algo: ${this.updateAlgo}`);
-    this.elDropdown = container.querySelector<HTMLElement>(':scope > .ui.dropdown');
-    this.elList = container.querySelector<HTMLElement>(':scope > .ui.list');
-    this.elComboValue = container.querySelector<HTMLInputElement>(':scope > .combo-value');
+    this.elDropdown = container.querySelector<HTMLElement>(':scope > .ui.dropdown')!;
+    this.elList = container.querySelector<HTMLElement>(':scope > .ui.list')!;
+    this.elComboValue = container.querySelector<HTMLInputElement>(':scope > .combo-value')!;
   }
 
   collectCheckedValues() {
-    return Array.from(this.elDropdown.querySelectorAll('.menu > .item.checked'), (el) => el.getAttribute('data-value'));
+    return Array.from(this.elDropdown.querySelectorAll('.menu > .item.checked'), (el) => el.getAttribute('data-value')!);
   }
 
   updateUiList(changedValues: Array<string>) {
-    const elEmptyTip = this.elList.querySelector('.item.empty-list');
+    const elEmptyTip = this.elList.querySelector('.item.empty-list')!;
     queryElemChildren(this.elList, '.item:not(.empty-list)', (el) => el.remove());
     for (const value of changedValues) {
       const el = this.elDropdown.querySelector<HTMLElement>(`.menu > .item[data-value="${CSS.escape(value)}"]`);
diff --git a/web_src/js/features/repo-issue-sidebar.ts b/web_src/js/features/repo-issue-sidebar.ts
index 290e1ae000..2ff077e6db 100644
--- a/web_src/js/features/repo-issue-sidebar.ts
+++ b/web_src/js/features/repo-issue-sidebar.ts
@@ -8,10 +8,10 @@ function initBranchSelector() {
   if (!elSelectBranch) return;
 
   const urlUpdateIssueRef = elSelectBranch.getAttribute('data-url-update-issueref');
-  const elBranchMenu = elSelectBranch.querySelector('.reference-list-menu');
+  const elBranchMenu = elSelectBranch.querySelector('.reference-list-menu')!;
   queryElems(elBranchMenu, '.item:not(.no-select)', (el) => el.addEventListener('click', async function (e) {
     e.preventDefault();
-    const selectedValue = this.getAttribute('data-id'); // eg: "refs/heads/my-branch"
+    const selectedValue = this.getAttribute('data-id')!; // eg: "refs/heads/my-branch"
     const selectedText = this.getAttribute('data-name'); // eg: "my-branch"
     if (urlUpdateIssueRef) {
       // for existing issue, send request to update issue ref, and reload page
@@ -23,9 +23,9 @@ function initBranchSelector() {
       }
     } else {
       // for new issue, only update UI&form, do not send request/reload
-      const selectedHiddenSelector = this.getAttribute('data-id-selector');
-      document.querySelector<HTMLInputElement>(selectedHiddenSelector).value = selectedValue;
-      elSelectBranch.querySelector('.text-branch-name').textContent = selectedText;
+      const selectedHiddenSelector = this.getAttribute('data-id-selector')!;
+      document.querySelector<HTMLInputElement>(selectedHiddenSelector)!.value = selectedValue;
+      elSelectBranch.querySelector('.text-branch-name')!.textContent = selectedText;
     }
   }));
 }
@@ -33,7 +33,7 @@ function initBranchSelector() {
 function initRepoIssueDue() {
   const form = document.querySelector<HTMLFormElement>('.issue-due-form');
   if (!form) return;
-  const deadline = form.querySelector<HTMLInputElement>('input[name=deadline]');
+  const deadline = form.querySelector<HTMLInputElement>('input[name=deadline]')!;
   document.querySelector('.issue-due-edit')?.addEventListener('click', () => {
     toggleElem(form);
   });
diff --git a/web_src/js/features/repo-issue.ts b/web_src/js/features/repo-issue.ts
index bacdae5350..7145936ed1 100644
--- a/web_src/js/features/repo-issue.ts
+++ b/web_src/js/features/repo-issue.ts
@@ -7,7 +7,6 @@ import {
   queryElems,
   showElem,
   toggleElem,
-  type DOMEvent,
 } from '../utils/dom.ts';
 import {setFileFolding} from './file-fold.ts';
 import {ComboMarkdownEditor, getComboMarkdownEditor, initComboMarkdownEditor} from './comp/ComboMarkdownEditor.ts';
@@ -67,7 +66,7 @@ function initRepoIssueLabelFilter(elDropdown: HTMLElement) {
   const excludeLabel = (e: MouseEvent | KeyboardEvent, item: Element) => {
     e.preventDefault();
     e.stopPropagation();
-    const labelId = item.getAttribute('data-label-id');
+    const labelId = item.getAttribute('data-label-id')!;
     let labelIds: string[] = queryLabels ? queryLabels.split(',') : [];
     labelIds = labelIds.filter((id) => Math.abs(parseInt(id)) !== Math.abs(parseInt(labelId)));
     labelIds.push(`-${labelId}`);
@@ -89,14 +88,14 @@ function initRepoIssueLabelFilter(elDropdown: HTMLElement) {
     }
   });
   // no "labels" query parameter means "all issues"
-  elDropdown.querySelector('.label-filter-query-default').classList.toggle('selected', queryLabels === '');
+  elDropdown.querySelector('.label-filter-query-default')!.classList.toggle('selected', queryLabels === '');
   // "labels=0" query parameter means "issues without label"
-  elDropdown.querySelector('.label-filter-query-not-set').classList.toggle('selected', queryLabels === '0');
+  elDropdown.querySelector('.label-filter-query-not-set')!.classList.toggle('selected', queryLabels === '0');
 
   // prepare to process "archived" labels
   const elShowArchivedLabel = elDropdown.querySelector('.label-filter-archived-toggle');
   if (!elShowArchivedLabel) return;
-  const elShowArchivedInput = elShowArchivedLabel.querySelector<HTMLInputElement>('input');
+  const elShowArchivedInput = elShowArchivedLabel.querySelector<HTMLInputElement>('input')!;
   elShowArchivedInput.checked = showArchivedLabels;
   const archivedLabels = elDropdown.querySelectorAll('.item[data-is-archived]');
   // if no archived labels, hide the toggle and return
@@ -107,7 +106,7 @@ function initRepoIssueLabelFilter(elDropdown: HTMLElement) {
 
   // show the archived labels if the toggle is checked or the label is selected
   for (const label of archivedLabels) {
-    toggleElem(label, showArchivedLabels || selectedLabelIds.has(label.getAttribute('data-label-id')));
+    toggleElem(label, showArchivedLabels || selectedLabelIds.has(label.getAttribute('data-label-id')!));
   }
   // update the url when the toggle is changed and reload
   elShowArchivedInput.addEventListener('input', () => {
@@ -127,14 +126,14 @@ export function initRepoIssueFilterItemLabel() {
 
 export function initRepoIssueCommentDelete() {
   // Delete comment
-  document.addEventListener('click', async (e: DOMEvent<MouseEvent>) => {
-    if (!e.target.matches('.delete-comment')) return;
+  document.addEventListener('click', async (e) => {
+    if (!(e.target as HTMLElement).matches('.delete-comment')) return;
     e.preventDefault();
 
-    const deleteButton = e.target;
-    if (window.confirm(deleteButton.getAttribute('data-locale'))) {
+    const deleteButton = e.target as HTMLElement;
+    if (window.confirm(deleteButton.getAttribute('data-locale')!)) {
       try {
-        const response = await POST(deleteButton.getAttribute('data-url'));
+        const response = await POST(deleteButton.getAttribute('data-url')!);
         if (!response.ok) throw new Error('Failed to delete comment');
 
         const conversationHolder = deleteButton.closest('.conversation-holder');
@@ -143,8 +142,8 @@ export function initRepoIssueCommentDelete() {
 
         // Check if this was a pending comment.
         if (conversationHolder?.querySelector('.pending-label')) {
-          const counter = document.querySelector('#review-box .review-comments-counter');
-          let num = parseInt(counter?.getAttribute('data-pending-comment-number')) - 1 || 0;
+          const counter = document.querySelector('#review-box .review-comments-counter')!;
+          let num = parseInt(counter?.getAttribute('data-pending-comment-number') || '') - 1 || 0;
           num = Math.max(num, 0);
           counter.setAttribute('data-pending-comment-number', String(num));
           counter.textContent = String(num);
@@ -162,9 +161,9 @@ export function initRepoIssueCommentDelete() {
           // on the Conversation page, there is no parent "tr", so no need to do anything for "add-code-comment"
           if (lineType) {
             if (lineType === 'same') {
-              document.querySelector(`[data-path="${path}"] .add-code-comment[data-idx="${idx}"]`).classList.remove('tw-invisible');
+              document.querySelector(`[data-path="${path}"] .add-code-comment[data-idx="${idx}"]`)!.classList.remove('tw-invisible');
             } else {
-              document.querySelector(`[data-path="${path}"] .add-code-comment[data-side="${side}"][data-idx="${idx}"]`).classList.remove('tw-invisible');
+              document.querySelector(`[data-path="${path}"] .add-code-comment[data-side="${side}"][data-idx="${idx}"]`)!.classList.remove('tw-invisible');
             }
           }
           conversationHolder.remove();
@@ -184,13 +183,13 @@ export function initRepoIssueCommentDelete() {
 
 export function initRepoIssueCodeCommentCancel() {
   // Cancel inline code comment
-  document.addEventListener('click', (e: DOMEvent<MouseEvent>) => {
-    if (!e.target.matches('.cancel-code-comment')) return;
+  document.addEventListener('click', (e) => {
+    if (!(e.target as HTMLElement).matches('.cancel-code-comment')) return;
 
-    const form = e.target.closest('form');
+    const form = (e.target as HTMLElement).closest('form')!;
     if (form?.classList.contains('comment-form')) {
       hideElem(form);
-      showElem(form.closest('.comment-code-cloud')?.querySelectorAll('button.comment-form-reply'));
+      showElem(form.closest('.comment-code-cloud')!.querySelectorAll('button.comment-form-reply'));
     } else {
       form.closest('.comment-code-cloud')?.remove();
     }
@@ -198,9 +197,9 @@ export function initRepoIssueCodeCommentCancel() {
 }
 
 export function initRepoPullRequestAllowMaintainerEdit() {
-  const wrapper = document.querySelector('#allow-edits-from-maintainers');
+  const wrapper = document.querySelector('#allow-edits-from-maintainers')!;
   if (!wrapper) return;
-  const checkbox = wrapper.querySelector<HTMLInputElement>('input[type="checkbox"]');
+  const checkbox = wrapper.querySelector<HTMLInputElement>('input[type="checkbox"]')!;
   checkbox.addEventListener('input', async () => {
     const url = `${wrapper.getAttribute('data-url')}/set_allow_maintainer_edit`;
     wrapper.classList.add('is-loading');
@@ -216,7 +215,7 @@ export function initRepoPullRequestAllowMaintainerEdit() {
     } catch (error) {
       checkbox.checked = !checkbox.checked;
       console.error(error);
-      showTemporaryTooltip(wrapper, wrapper.getAttribute('data-prompt-error'));
+      showTemporaryTooltip(wrapper, wrapper.getAttribute('data-prompt-error')!);
     } finally {
       wrapper.classList.remove('is-loading');
     }
@@ -226,7 +225,7 @@ export function initRepoPullRequestAllowMaintainerEdit() {
 export function initRepoIssueComments() {
   if (!document.querySelector('.repository.view.issue .timeline')) return;
 
-  document.addEventListener('click', (e: DOMEvent<MouseEvent>) => {
+  document.addEventListener('click', (e: Event) => {
     const urlTarget = document.querySelector(':target');
     if (!urlTarget) return;
 
@@ -235,22 +234,22 @@ export function initRepoIssueComments() {
 
     if (!/^(issue|pull)(comment)?-\d+$/.test(urlTargetId)) return;
 
-    if (!e.target.closest(`#${urlTargetId}`)) {
+    if (!(e.target as HTMLElement).closest(`#${urlTargetId}`)) {
       // if the user clicks outside the comment, remove the hash from the url
       // use empty hash and state to avoid scrolling
       window.location.hash = ' ';
-      window.history.pushState(null, null, ' ');
+      window.history.pushState(null, '', ' ');
     }
   });
 }
 
 export async function handleReply(el: HTMLElement) {
-  const form = el.closest('.comment-code-cloud').querySelector('.comment-form');
+  const form = el.closest('.comment-code-cloud')!.querySelector('.comment-form')!;
   const textarea = form.querySelector('textarea');
 
   hideElem(el);
   showElem(form);
-  const editor = getComboMarkdownEditor(textarea) ?? await initComboMarkdownEditor(form.querySelector('.combo-markdown-editor'));
+  const editor = getComboMarkdownEditor(textarea) ?? await initComboMarkdownEditor(form.querySelector('.combo-markdown-editor')!);
   editor.focus();
   return editor;
 }
@@ -269,7 +268,7 @@ export function initRepoPullRequestReview() {
         showElem(`#code-comments-${id}, #code-preview-${id}, #hide-outdated-${id}`);
         // if the comment box is folded, expand it
         if (ancestorDiffBox?.getAttribute('data-folded') === 'true') {
-          setFileFolding(ancestorDiffBox, ancestorDiffBox.querySelector('.fold-file'), false);
+          setFileFolding(ancestorDiffBox, ancestorDiffBox.querySelector('.fold-file')!, false);
         }
       }
       // set scrollRestoration to 'manual' when there is a hash in url, so that the scroll position will not be remembered after refreshing
@@ -317,18 +316,18 @@ export function initRepoPullRequestReview() {
       interactive: true,
       hideOnClick: true,
     });
-    elReviewPanel.querySelector('.close').addEventListener('click', () => tippy.hide());
+    elReviewPanel.querySelector('.close')!.addEventListener('click', () => tippy.hide());
   }
 
   addDelegatedEventListener(document, 'click', '.add-code-comment', async (el, e) => {
     e.preventDefault();
 
     const isSplit = el.closest('.code-diff')?.classList.contains('code-diff-split');
-    const side = el.getAttribute('data-side');
-    const idx = el.getAttribute('data-idx');
+    const side = el.getAttribute('data-side')!;
+    const idx = el.getAttribute('data-idx')!;
     const path = el.closest('[data-path]')?.getAttribute('data-path');
-    const tr = el.closest('tr');
-    const lineType = tr.getAttribute('data-line-type');
+    const tr = el.closest('tr')!;
+    const lineType = tr.getAttribute('data-line-type')!;
 
     let ntr = tr.nextElementSibling;
     if (!ntr?.classList.contains('add-comment')) {
@@ -343,15 +342,15 @@ export function initRepoPullRequestReview() {
         </tr>`);
       tr.after(ntr);
     }
-    const td = ntr.querySelector(`.add-comment-${side}`);
+    const td = ntr.querySelector(`.add-comment-${side}`)!;
     const commentCloud = td.querySelector('.comment-code-cloud');
     if (!commentCloud && !ntr.querySelector('button[name="pending_review"]')) {
-      const response = await GET(el.closest('[data-new-comment-url]')?.getAttribute('data-new-comment-url'));
+      const response = await GET(el.closest('[data-new-comment-url]')?.getAttribute('data-new-comment-url') ?? '');
       td.innerHTML = await response.text();
-      td.querySelector<HTMLInputElement>("input[name='line']").value = idx;
-      td.querySelector<HTMLInputElement>("input[name='side']").value = (side === 'left' ? 'previous' : 'proposed');
-      td.querySelector<HTMLInputElement>("input[name='path']").value = path;
-      const editor = await initComboMarkdownEditor(td.querySelector<HTMLElement>('.combo-markdown-editor'));
+      td.querySelector<HTMLInputElement>("input[name='line']")!.value = idx;
+      td.querySelector<HTMLInputElement>("input[name='side']")!.value = (side === 'left' ? 'previous' : 'proposed');
+      td.querySelector<HTMLInputElement>("input[name='path']")!.value = String(path);
+      const editor = await initComboMarkdownEditor(td.querySelector<HTMLElement>('.combo-markdown-editor')!);
       editor.focus();
     }
   });
@@ -360,7 +359,7 @@ export function initRepoPullRequestReview() {
 export function initRepoIssueReferenceIssue() {
   const elDropdown = document.querySelector('.issue_reference_repository_search');
   if (!elDropdown) return;
-  const form = elDropdown.closest('form');
+  const form = elDropdown.closest('form')!;
   fomanticQuery(elDropdown).dropdown({
     fullTextSearch: true,
     apiSettings: {
@@ -389,10 +388,10 @@ export function initRepoIssueReferenceIssue() {
     const target = el.getAttribute('data-target');
     const content = document.querySelector(`#${target}`)?.textContent ?? '';
     const poster = el.getAttribute('data-poster-username');
-    const reference = toAbsoluteUrl(el.getAttribute('data-reference'));
-    const modalSelector = el.getAttribute('data-modal');
-    const modal = document.querySelector(modalSelector);
-    const textarea = modal.querySelector<HTMLTextAreaElement>('textarea[name="content"]');
+    const reference = toAbsoluteUrl(el.getAttribute('data-reference')!);
+    const modalSelector = el.getAttribute('data-modal')!;
+    const modal = document.querySelector(modalSelector)!;
+    const textarea = modal.querySelector<HTMLTextAreaElement>('textarea[name="content"]')!;
     textarea.value = `${content}\n\n_Originally posted by @${poster} in ${reference}_`;
     fomanticQuery(modal).modal('show');
   });
@@ -402,8 +401,8 @@ export function initRepoIssueWipNewTitle() {
   // Toggle WIP for new PR
   queryElems(document, '.title_wip_desc > a', (el) => el.addEventListener('click', (e) => {
     e.preventDefault();
-    const wipPrefixes = JSON.parse(el.closest('.title_wip_desc').getAttribute('data-wip-prefixes'));
-    const titleInput = document.querySelector<HTMLInputElement>('#issue_title');
+    const wipPrefixes = JSON.parse(el.closest('.title_wip_desc')!.getAttribute('data-wip-prefixes')!);
+    const titleInput = document.querySelector<HTMLInputElement>('#issue_title')!;
     const titleValue = titleInput.value;
     for (const prefix of wipPrefixes) {
       if (titleValue.startsWith(prefix.toUpperCase())) {
@@ -419,8 +418,8 @@ export function initRepoIssueWipToggle() {
   registerGlobalInitFunc('initPullRequestWipToggle', (toggleWip) => toggleWip.addEventListener('click', async (e) => {
     e.preventDefault();
     const title = toggleWip.getAttribute('data-title');
-    const wipPrefix = toggleWip.getAttribute('data-wip-prefix');
-    const updateUrl = toggleWip.getAttribute('data-update-url');
+    const wipPrefix = toggleWip.getAttribute('data-wip-prefix')!;
+    const updateUrl = toggleWip.getAttribute('data-update-url')!;
 
     const params = new URLSearchParams();
     params.append('title', title?.startsWith(wipPrefix) ? title.slice(wipPrefix.length).trim() : `${wipPrefix.trim()} ${title}`);
@@ -434,13 +433,13 @@ export function initRepoIssueWipToggle() {
 }
 
 export function initRepoIssueTitleEdit() {
-  const issueTitleDisplay = document.querySelector('#issue-title-display');
+  const issueTitleDisplay = document.querySelector('#issue-title-display')!;
   const issueTitleEditor = document.querySelector<HTMLFormElement>('#issue-title-editor');
   if (!issueTitleEditor) return;
 
-  const issueTitleInput = issueTitleEditor.querySelector('input');
-  const oldTitle = issueTitleInput.getAttribute('data-old-title');
-  issueTitleDisplay.querySelector('#issue-title-edit-show').addEventListener('click', () => {
+  const issueTitleInput = issueTitleEditor.querySelector('input')!;
+  const oldTitle = issueTitleInput.getAttribute('data-old-title')!;
+  issueTitleDisplay.querySelector('#issue-title-edit-show')!.addEventListener('click', () => {
     hideElem(issueTitleDisplay);
     hideElem('#pull-desc-display');
     showElem(issueTitleEditor);
@@ -450,7 +449,7 @@ export function initRepoIssueTitleEdit() {
     }
     issueTitleInput.focus();
   });
-  issueTitleEditor.querySelector('.ui.cancel.button').addEventListener('click', () => {
+  issueTitleEditor.querySelector('.ui.cancel.button')!.addEventListener('click', () => {
     hideElem(issueTitleEditor);
     hideElem('#pull-desc-editor');
     showElem(issueTitleDisplay);
@@ -460,22 +459,22 @@ export function initRepoIssueTitleEdit() {
   const pullDescEditor = document.querySelector('#pull-desc-editor'); // it may not exist for a merged PR
   const prTargetUpdateUrl = pullDescEditor?.getAttribute('data-target-update-url');
 
-  const editSaveButton = issueTitleEditor.querySelector('.ui.primary.button');
+  const editSaveButton = issueTitleEditor.querySelector('.ui.primary.button')!;
   issueTitleEditor.addEventListener('submit', async (e) => {
     e.preventDefault();
     const newTitle = issueTitleInput.value.trim();
     try {
       if (newTitle && newTitle !== oldTitle) {
-        const resp = await POST(editSaveButton.getAttribute('data-update-url'), {data: new URLSearchParams({title: newTitle})});
+        const resp = await POST(editSaveButton.getAttribute('data-update-url')!, {data: new URLSearchParams({title: newTitle})});
         if (!resp.ok) {
           throw new Error(`Failed to update issue title: ${resp.statusText}`);
         }
       }
       if (prTargetUpdateUrl) {
-        const newTargetBranch = document.querySelector('#pull-target-branch').getAttribute('data-branch');
-        const oldTargetBranch = document.querySelector('#branch_target').textContent;
+        const newTargetBranch = document.querySelector('#pull-target-branch')!.getAttribute('data-branch');
+        const oldTargetBranch = document.querySelector('#branch_target')!.textContent;
         if (newTargetBranch !== oldTargetBranch) {
-          const resp = await POST(prTargetUpdateUrl, {data: new URLSearchParams({target_branch: newTargetBranch})});
+          const resp = await POST(prTargetUpdateUrl, {data: new URLSearchParams({target_branch: String(newTargetBranch)})});
           if (!resp.ok) {
             throw new Error(`Failed to update PR target branch: ${resp.statusText}`);
           }
@@ -491,12 +490,12 @@ export function initRepoIssueTitleEdit() {
 }
 
 export function initRepoIssueBranchSelect() {
-  document.querySelector<HTMLElement>('#branch-select')?.addEventListener('click', (e: DOMEvent<MouseEvent>) => {
-    const el = e.target.closest('.item[data-branch]');
+  document.querySelector<HTMLElement>('#branch-select')?.addEventListener('click', (e: Event) => {
+    const el = (e.target as HTMLElement).closest('.item[data-branch]');
     if (!el) return;
-    const pullTargetBranch = document.querySelector('#pull-target-branch');
+    const pullTargetBranch = document.querySelector('#pull-target-branch')!;
     const baseName = pullTargetBranch.getAttribute('data-basename');
-    const branchNameNew = el.getAttribute('data-branch');
+    const branchNameNew = el.getAttribute('data-branch')!;
     const branchNameOld = pullTargetBranch.getAttribute('data-branch');
     pullTargetBranch.textContent = pullTargetBranch.textContent.replace(`${baseName}:${branchNameOld}`, `${baseName}:${branchNameNew}`);
     pullTargetBranch.setAttribute('data-branch', branchNameNew);
@@ -507,7 +506,7 @@ async function initSingleCommentEditor(commentForm: HTMLFormElement) {
   // pages:
   // * normal new issue/pr page: no status-button, no comment-button (there is only a normal submit button which can submit empty content)
   // * issue/pr view page: with comment form, has status-button and comment-button
-  const editor = await initComboMarkdownEditor(commentForm.querySelector('.combo-markdown-editor'));
+  const editor = await initComboMarkdownEditor(commentForm.querySelector('.combo-markdown-editor')!);
   const statusButton = document.querySelector<HTMLButtonElement>('#status-button');
   const commentButton = document.querySelector<HTMLButtonElement>('#comment-button');
   const syncUiState = () => {
@@ -531,9 +530,9 @@ function initIssueTemplateCommentEditors(commentForm: HTMLFormElement) {
   const comboFields = commentForm.querySelectorAll<HTMLElement>('.combo-editor-dropzone');
 
   const initCombo = async (elCombo: HTMLElement) => {
-    const fieldTextarea = elCombo.querySelector<HTMLTextAreaElement>('.form-field-real');
-    const dropzoneContainer = elCombo.querySelector<HTMLElement>('.form-field-dropzone');
-    const markdownEditor = elCombo.querySelector<HTMLElement>('.combo-markdown-editor');
+    const fieldTextarea = elCombo.querySelector<HTMLTextAreaElement>('.form-field-real')!;
+    const dropzoneContainer = elCombo.querySelector<HTMLElement>('.form-field-dropzone')!;
+    const markdownEditor = elCombo.querySelector<HTMLElement>('.combo-markdown-editor')!;
 
     const editor = await initComboMarkdownEditor(markdownEditor);
     editor.container.addEventListener(ComboMarkdownEditor.EventEditorContentChanged, () => fieldTextarea.value = editor.value());
@@ -544,7 +543,7 @@ function initIssueTemplateCommentEditors(commentForm: HTMLFormElement) {
       hideElem(commentForm.querySelectorAll('.combo-editor-dropzone .combo-markdown-editor'));
       queryElems(commentForm, '.combo-editor-dropzone .form-field-dropzone', (dropzoneContainer) => {
         // if "form-field-dropzone" exists, then "dropzone" must also exist
-        const dropzone = dropzoneContainer.querySelector<HTMLElement>('.dropzone').dropzone;
+        const dropzone = dropzoneContainer.querySelector<HTMLElement>('.dropzone')!.dropzone;
         const hasUploadedFiles = dropzone.files.length !== 0;
         toggleElem(dropzoneContainer, hasUploadedFiles);
       });
diff --git a/web_src/js/features/repo-legacy.ts b/web_src/js/features/repo-legacy.ts
index 249d181b25..fc92242b40 100644
--- a/web_src/js/features/repo-legacy.ts
+++ b/web_src/js/features/repo-legacy.ts
@@ -30,8 +30,8 @@ export function initBranchSelectorTabs() {
   for (const elSelectBranch of elSelectBranches) {
     queryElems(elSelectBranch, '.reference.column', (el) => el.addEventListener('click', () => {
       hideElem(elSelectBranch.querySelectorAll('.scrolling.reference-list-menu'));
-      showElem(el.getAttribute('data-target'));
-      queryElemChildren(el.parentNode, '.branch-tag-item', (el) => el.classList.remove('active'));
+      showElem(el.getAttribute('data-target')!);
+      queryElemChildren(el.parentNode!, '.branch-tag-item', (el) => el.classList.remove('active'));
       el.classList.add('active');
     }));
   }
diff --git a/web_src/js/features/repo-migrate.ts b/web_src/js/features/repo-migrate.ts
index 0788f83215..556f049246 100644
--- a/web_src/js/features/repo-migrate.ts
+++ b/web_src/js/features/repo-migrate.ts
@@ -1,4 +1,4 @@
-import {hideElem, showElem, type DOMEvent} from '../utils/dom.ts';
+import {hideElem, showElem} from '../utils/dom.ts';
 import {GET, POST} from '../modules/fetch.ts';
 
 export function initRepoMigrationStatusChecker() {
@@ -18,7 +18,7 @@ export function initRepoMigrationStatusChecker() {
 
     // for all status
     if (data.message) {
-      document.querySelector('#repo_migrating_progress_message').textContent = data.message;
+      document.querySelector('#repo_migrating_progress_message')!.textContent = data.message;
     }
 
     // TaskStatusFinished
@@ -34,7 +34,7 @@ export function initRepoMigrationStatusChecker() {
       showElem('#repo_migrating_retry');
       showElem('#repo_migrating_failed');
       showElem('#repo_migrating_failed_image');
-      document.querySelector('#repo_migrating_failed_error').textContent = data.message;
+      document.querySelector('#repo_migrating_failed_error')!.textContent = data.message;
       return false;
     }
 
@@ -55,7 +55,7 @@ export function initRepoMigrationStatusChecker() {
   syncTaskStatus(); // no await
 }
 
-async function doMigrationRetry(e: DOMEvent<MouseEvent>) {
-  await POST(e.target.getAttribute('data-migrating-task-retry-url'));
+async function doMigrationRetry(e: Event) {
+  await POST((e.target as HTMLElement).getAttribute('data-migrating-task-retry-url')!);
   window.location.reload();
 }
diff --git a/web_src/js/features/repo-migration.ts b/web_src/js/features/repo-migration.ts
index 9f086bb9d3..7376ff7fa4 100644
--- a/web_src/js/features/repo-migration.ts
+++ b/web_src/js/features/repo-migration.ts
@@ -7,8 +7,8 @@ const pass = document.querySelector<HTMLInputElement>('#auth_password');
 const token = document.querySelector<HTMLInputElement>('#auth_token');
 const mirror = document.querySelector<HTMLInputElement>('#mirror');
 const lfs = document.querySelector<HTMLInputElement>('#lfs');
-const lfsSettings = document.querySelector<HTMLElement>('#lfs_settings');
-const lfsEndpoint = document.querySelector<HTMLElement>('#lfs_endpoint');
+const lfsSettings = document.querySelector<HTMLElement>('#lfs_settings')!;
+const lfsEndpoint = document.querySelector<HTMLElement>('#lfs_endpoint')!;
 const items = document.querySelectorAll<HTMLInputElement>('#migrate_items input[type=checkbox]');
 
 export function initRepoMigration() {
diff --git a/web_src/js/features/repo-milestone.ts b/web_src/js/features/repo-milestone.ts
index ee704ea2e0..ceca8e0b46 100644
--- a/web_src/js/features/repo-milestone.ts
+++ b/web_src/js/features/repo-milestone.ts
@@ -2,8 +2,8 @@ export function initRepoMilestone() {
   const page = document.querySelector('.repository.new.milestone');
   if (!page) return;
 
-  const deadline = page.querySelector<HTMLInputElement>('form input[name=deadline]');
-  document.querySelector('#milestone-clear-deadline').addEventListener('click', () => {
+  const deadline = page.querySelector<HTMLInputElement>('form input[name=deadline]')!;
+  document.querySelector('#milestone-clear-deadline')!.addEventListener('click', () => {
     deadline.value = '';
   });
 }
diff --git a/web_src/js/features/repo-new.ts b/web_src/js/features/repo-new.ts
index e2aa13f490..b690ace0f7 100644
--- a/web_src/js/features/repo-new.ts
+++ b/web_src/js/features/repo-new.ts
@@ -6,13 +6,13 @@ import {sanitizeRepoName} from './repo-common.ts';
 const {appSubUrl} = window.config;
 
 function initRepoNewTemplateSearch(form: HTMLFormElement) {
-  const elSubmitButton = querySingleVisibleElem<HTMLInputElement>(form, '.ui.primary.button');
-  const elCreateRepoErrorMessage = form.querySelector('#create-repo-error-message');
-  const elRepoOwnerDropdown = form.querySelector('#repo_owner_dropdown');
-  const elRepoTemplateDropdown = form.querySelector<HTMLInputElement>('#repo_template_search');
-  const inputRepoTemplate = form.querySelector<HTMLInputElement>('#repo_template');
-  const elTemplateUnits = form.querySelector('#template_units');
-  const elNonTemplate = form.querySelector('#non_template');
+  const elSubmitButton = querySingleVisibleElem<HTMLInputElement>(form, '.ui.primary.button')!;
+  const elCreateRepoErrorMessage = form.querySelector('#create-repo-error-message')!;
+  const elRepoOwnerDropdown = form.querySelector('#repo_owner_dropdown')!;
+  const elRepoTemplateDropdown = form.querySelector<HTMLInputElement>('#repo_template_search')!;
+  const inputRepoTemplate = form.querySelector<HTMLInputElement>('#repo_template')!;
+  const elTemplateUnits = form.querySelector('#template_units')!;
+  const elNonTemplate = form.querySelector('#non_template')!;
   const checkTemplate = function () {
     const hasSelectedTemplate = inputRepoTemplate.value !== '' && inputRepoTemplate.value !== '0';
     toggleElem(elTemplateUnits, hasSelectedTemplate);
@@ -62,10 +62,10 @@ export function initRepoNew() {
   const pageContent = document.querySelector('.page-content.repository.new-repo');
   if (!pageContent) return;
 
-  const form = document.querySelector<HTMLFormElement>('.new-repo-form');
-  const inputGitIgnores = form.querySelector<HTMLInputElement>('input[name="gitignores"]');
-  const inputLicense = form.querySelector<HTMLInputElement>('input[name="license"]');
-  const inputAutoInit = form.querySelector<HTMLInputElement>('input[name="auto_init"]');
+  const form = document.querySelector<HTMLFormElement>('.new-repo-form')!;
+  const inputGitIgnores = form.querySelector<HTMLInputElement>('input[name="gitignores"]')!;
+  const inputLicense = form.querySelector<HTMLInputElement>('input[name="license"]')!;
+  const inputAutoInit = form.querySelector<HTMLInputElement>('input[name="auto_init"]')!;
   const updateUiAutoInit = () => {
     inputAutoInit.checked = Boolean(inputGitIgnores.value || inputLicense.value);
   };
@@ -73,13 +73,13 @@ export function initRepoNew() {
   inputLicense.addEventListener('change', updateUiAutoInit);
   updateUiAutoInit();
 
-  const inputRepoName = form.querySelector<HTMLInputElement>('input[name="repo_name"]');
-  const inputPrivate = form.querySelector<HTMLInputElement>('input[name="private"]');
+  const inputRepoName = form.querySelector<HTMLInputElement>('input[name="repo_name"]')!;
+  const inputPrivate = form.querySelector<HTMLInputElement>('input[name="private"]')!;
   const updateUiRepoName = () => {
     const helps = form.querySelectorAll(`.help[data-help-for-repo-name]`);
     hideElem(helps);
     let help = form.querySelector(`.help[data-help-for-repo-name="${CSS.escape(inputRepoName.value)}"]`);
-    if (!help) help = form.querySelector(`.help[data-help-for-repo-name=""]`);
+    if (!help) help = form.querySelector(`.help[data-help-for-repo-name=""]`)!;
     showElem(help);
     const repoNamePreferPrivate: Record<string, boolean> = {'.profile': false, '.profile-private': true};
     const preferPrivate = repoNamePreferPrivate[inputRepoName.value];
diff --git a/web_src/js/features/repo-projects.ts b/web_src/js/features/repo-projects.ts
index ad0feb6101..b5dfd51b9b 100644
--- a/web_src/js/features/repo-projects.ts
+++ b/web_src/js/features/repo-projects.ts
@@ -7,9 +7,9 @@ import type {SortableEvent} from 'sortablejs';
 import {toggleFullScreen} from '../utils.ts';
 
 function updateIssueCount(card: HTMLElement): void {
-  const parent = card.parentElement;
+  const parent = card.parentElement!;
   const count = parent.querySelectorAll('.issue-card').length;
-  parent.querySelector('.project-column-issue-count').textContent = String(count);
+  parent.querySelector('.project-column-issue-count')!.textContent = String(count);
 }
 
 async function moveIssue({item, from, to, oldIndex}: SortableEvent): Promise<void> {
@@ -19,7 +19,7 @@ async function moveIssue({item, from, to, oldIndex}: SortableEvent): Promise<voi
 
   const columnSorting = {
     issues: Array.from(columnCards, (card, i) => ({
-      issueID: parseInt(card.getAttribute('data-issue')),
+      issueID: parseInt(card.getAttribute('data-issue')!),
       sorting: i,
     })),
   };
@@ -30,13 +30,15 @@ async function moveIssue({item, from, to, oldIndex}: SortableEvent): Promise<voi
     });
   } catch (error) {
     console.error(error);
-    from.insertBefore(item, from.children[oldIndex]);
+    if (oldIndex !== undefined) {
+      from.insertBefore(item, from.children[oldIndex]);
+    }
   }
 }
 
 async function initRepoProjectSortable(): Promise<void> {
   // the HTML layout is: #project-board.board > .project-column .cards > .issue-card
-  const mainBoard = document.querySelector('#project-board');
+  const mainBoard = document.querySelector('#project-board')!;
   let boardColumns = mainBoard.querySelectorAll<HTMLElement>('.project-column');
   createSortable(mainBoard, {
     group: 'project-column',
@@ -49,13 +51,13 @@ async function initRepoProjectSortable(): Promise<void> {
 
       const columnSorting = {
         columns: Array.from(boardColumns, (column, i) => ({
-          columnID: parseInt(column.getAttribute('data-id')),
+          columnID: parseInt(column.getAttribute('data-id')!),
           sorting: i,
         })),
       };
 
       try {
-        await POST(mainBoard.getAttribute('data-url'), {
+        await POST(mainBoard.getAttribute('data-url')!, {
           data: columnSorting,
         });
       } catch (error) {
@@ -65,7 +67,7 @@ async function initRepoProjectSortable(): Promise<void> {
   });
 
   for (const boardColumn of boardColumns) {
-    const boardCardList = boardColumn.querySelector('.cards');
+    const boardCardList = boardColumn.querySelector('.cards')!;
     createSortable(boardCardList, {
       group: 'shared',
       onAdd: moveIssue, // eslint-disable-line @typescript-eslint/no-misused-promises
@@ -77,12 +79,12 @@ async function initRepoProjectSortable(): Promise<void> {
 }
 
 function initRepoProjectColumnEdit(writableProjectBoard: Element): void {
-  const elModal = document.querySelector<HTMLElement>('.ui.modal#project-column-modal-edit');
-  const elForm = elModal.querySelector<HTMLFormElement>('form');
+  const elModal = document.querySelector<HTMLElement>('.ui.modal#project-column-modal-edit')!;
+  const elForm = elModal.querySelector<HTMLFormElement>('form')!;
 
-  const elColumnId = elForm.querySelector<HTMLInputElement>('input[name="id"]');
-  const elColumnTitle = elForm.querySelector<HTMLInputElement>('input[name="title"]');
-  const elColumnColor = elForm.querySelector<HTMLInputElement>('input[name="color"]');
+  const elColumnId = elForm.querySelector<HTMLInputElement>('input[name="id"]')!;
+  const elColumnTitle = elForm.querySelector<HTMLInputElement>('input[name="title"]')!;
+  const elColumnColor = elForm.querySelector<HTMLInputElement>('input[name="color"]')!;
 
   const attrDataColumnId = 'data-modal-project-column-id';
   const attrDataColumnTitle = 'data-modal-project-column-title-input';
@@ -91,9 +93,9 @@ function initRepoProjectColumnEdit(writableProjectBoard: Element): void {
   // the "new" button is not in project board, so need to query from document
   queryElems(document, '.show-project-column-modal-edit', (el) => {
     el.addEventListener('click', () => {
-      elColumnId.value = el.getAttribute(attrDataColumnId);
-      elColumnTitle.value = el.getAttribute(attrDataColumnTitle);
-      elColumnColor.value = el.getAttribute(attrDataColumnColor);
+      elColumnId.value = el.getAttribute(attrDataColumnId)!;
+      elColumnTitle.value = el.getAttribute(attrDataColumnTitle)!;
+      elColumnColor.value = el.getAttribute(attrDataColumnColor)!;
       elColumnColor.dispatchEvent(new Event('input', {bubbles: true})); // trigger the color picker
     });
   });
@@ -116,12 +118,12 @@ function initRepoProjectColumnEdit(writableProjectBoard: Element): void {
       }
 
       // update the newly saved column title and color in the project board (to avoid reload)
-      const elEditButton = writableProjectBoard.querySelector<HTMLButtonElement>(`.show-project-column-modal-edit[${attrDataColumnId}="${columnId}"]`);
+      const elEditButton = writableProjectBoard.querySelector<HTMLButtonElement>(`.show-project-column-modal-edit[${attrDataColumnId}="${columnId}"]`)!;
       elEditButton.setAttribute(attrDataColumnTitle, elColumnTitle.value);
       elEditButton.setAttribute(attrDataColumnColor, elColumnColor.value);
 
-      const elBoardColumn = writableProjectBoard.querySelector<HTMLElement>(`.project-column[data-id="${columnId}"]`);
-      const elBoardColumnTitle = elBoardColumn.querySelector<HTMLElement>(`.project-column-title-text`);
+      const elBoardColumn = writableProjectBoard.querySelector<HTMLElement>(`.project-column[data-id="${columnId}"]`)!;
+      const elBoardColumnTitle = elBoardColumn.querySelector<HTMLElement>(`.project-column-title-text`)!;
       elBoardColumnTitle.textContent = elColumnTitle.value;
       if (elColumnColor.value) {
         const textColor = contrastColor(elColumnColor.value);
diff --git a/web_src/js/features/repo-release.ts b/web_src/js/features/repo-release.ts
index dfff090ba9..30680c543b 100644
--- a/web_src/js/features/repo-release.ts
+++ b/web_src/js/features/repo-release.ts
@@ -1,11 +1,11 @@
-import {hideElem, showElem, type DOMEvent} from '../utils/dom.ts';
+import {hideElem, showElem} from '../utils/dom.ts';
 
 export function initRepoRelease() {
-  document.addEventListener('click', (e: DOMEvent<MouseEvent>) => {
-    if (e.target.matches('.remove-rel-attach')) {
-      const uuid = e.target.getAttribute('data-uuid');
-      const id = e.target.getAttribute('data-id');
-      document.querySelector<HTMLInputElement>(`input[name='attachment-del-${uuid}']`).value = 'true';
+  document.addEventListener('click', (e: Event) => {
+    if ((e.target as HTMLElement).matches('.remove-rel-attach')) {
+      const uuid = (e.target as HTMLElement).getAttribute('data-uuid');
+      const id = (e.target as HTMLElement).getAttribute('data-id');
+      document.querySelector<HTMLInputElement>(`input[name='attachment-del-${uuid}']`)!.value = 'true';
       hideElem(`#attachment-${id}`);
     }
   });
@@ -21,17 +21,17 @@ function initTagNameEditor() {
   const el = document.querySelector('#tag-name-editor');
   if (!el) return;
 
-  const existingTags = JSON.parse(el.getAttribute('data-existing-tags'));
+  const existingTags = JSON.parse(el.getAttribute('data-existing-tags')!);
   if (!Array.isArray(existingTags)) return;
 
   const defaultTagHelperText = el.getAttribute('data-tag-helper');
   const newTagHelperText = el.getAttribute('data-tag-helper-new');
   const existingTagHelperText = el.getAttribute('data-tag-helper-existing');
 
-  const tagNameInput = document.querySelector<HTMLInputElement>('#tag-name');
+  const tagNameInput = document.querySelector<HTMLInputElement>('#tag-name')!;
   const hideTargetInput = function(tagNameInput: HTMLInputElement) {
     const value = tagNameInput.value;
-    const tagHelper = document.querySelector('#tag-helper');
+    const tagHelper = document.querySelector('#tag-helper')!;
     if (existingTags.includes(value)) {
       // If the tag already exists, hide the target branch selector.
       hideElem('#tag-target-selector');
diff --git a/web_src/js/features/repo-search.ts b/web_src/js/features/repo-search.ts
index 27609adfc9..d3a40286fe 100644
--- a/web_src/js/features/repo-search.ts
+++ b/web_src/js/features/repo-search.ts
@@ -1,17 +1,15 @@
-import type {DOMEvent} from '../utils/dom.ts';
-
 export function initRepositorySearch() {
   const repositorySearchForm = document.querySelector<HTMLFormElement>('#repo-search-form');
   if (!repositorySearchForm) return;
 
-  repositorySearchForm.addEventListener('change', (e: DOMEvent<Event, HTMLInputElement>) => {
+  repositorySearchForm.addEventListener('change', (e: Event) => {
     e.preventDefault();
 
     const params = new URLSearchParams();
     for (const [key, value] of new FormData(repositorySearchForm).entries()) {
       params.set(key, value.toString());
     }
-    if (e.target.name === 'clear-filter') {
+    if ((e.target as HTMLInputElement).name === 'clear-filter') {
       params.delete('archived');
       params.delete('fork');
       params.delete('mirror');
diff --git a/web_src/js/features/repo-settings-branches.test.ts b/web_src/js/features/repo-settings-branches.test.ts
index 526e279723..a353593f5c 100644
--- a/web_src/js/features/repo-settings-branches.test.ts
+++ b/web_src/js/features/repo-settings-branches.test.ts
@@ -56,8 +56,10 @@ describe('Repository Branch Settings', () => {
     vi.mocked(POST).mockResolvedValue({ok: true} as Response);
 
     // Mock createSortable to capture and execute the onEnd callback
-    vi.mocked(createSortable).mockImplementation(async (_el: Element, options: SortableOptions) => {
-      options.onEnd(new Event('SortableEvent') as SortableEvent);
+    vi.mocked(createSortable).mockImplementation(async (_el: Element, options: SortableOptions | undefined) => {
+      if (options?.onEnd) {
+        options.onEnd(new Event('SortableEvent') as SortableEvent);
+      }
       // @ts-expect-error: mock is incomplete
       return {destroy: vi.fn()} as Sortable;
     });
diff --git a/web_src/js/features/repo-settings-branches.ts b/web_src/js/features/repo-settings-branches.ts
index 40cdf9f981..8668af2e50 100644
--- a/web_src/js/features/repo-settings-branches.ts
+++ b/web_src/js/features/repo-settings-branches.ts
@@ -14,10 +14,10 @@ export function initRepoSettingsBranchesDrag() {
     onEnd: () => {
       (async () => {
         const itemElems = queryElemChildren(protectedBranchesList, '.item[data-id]');
-        const itemIds = Array.from(itemElems, (el) => parseInt(el.getAttribute('data-id')));
+        const itemIds = Array.from(itemElems, (el) => parseInt(el.getAttribute('data-id')!));
 
         try {
-          await POST(protectedBranchesList.getAttribute('data-update-priority-url'), {
+          await POST(protectedBranchesList.getAttribute('data-update-priority-url')!, {
             data: {
               ids: itemIds,
             },
diff --git a/web_src/js/features/repo-settings.ts b/web_src/js/features/repo-settings.ts
index 7a8df8af0f..ee2f17f4e0 100644
--- a/web_src/js/features/repo-settings.ts
+++ b/web_src/js/features/repo-settings.ts
@@ -10,16 +10,16 @@ const {appSubUrl, csrfToken} = window.config;
 function initRepoSettingsCollaboration() {
   // Change collaborator access mode
   for (const dropdownEl of queryElems(document, '.page-content.repository .ui.dropdown.access-mode')) {
-    const textEl = dropdownEl.querySelector(':scope > .text');
+    const textEl = dropdownEl.querySelector(':scope > .text')!;
     const $dropdown = fomanticQuery(dropdownEl);
     $dropdown.dropdown({
       async action(text: string, value: string) {
         dropdownEl.classList.add('is-loading', 'loading-icon-2px');
-        const lastValue = dropdownEl.getAttribute('data-last-value');
+        const lastValue = dropdownEl.getAttribute('data-last-value')!;
         $dropdown.dropdown('hide');
         try {
-          const uid = dropdownEl.getAttribute('data-uid');
-          await POST(dropdownEl.getAttribute('data-url'), {data: new URLSearchParams({uid, 'mode': value})});
+          const uid = dropdownEl.getAttribute('data-uid')!;
+          await POST(dropdownEl.getAttribute('data-url')!, {data: new URLSearchParams({uid, 'mode': value})});
           textEl.textContent = text;
           dropdownEl.setAttribute('data-last-value', value);
         } catch {
@@ -73,8 +73,8 @@ function initRepoSettingsSearchTeamBox() {
 
 function initRepoSettingsGitHook() {
   if (!document.querySelector('.page-content.repository.settings.edit.githook')) return;
-  const filename = document.querySelector('.hook-filename').textContent;
-  createMonaco(document.querySelector<HTMLTextAreaElement>('#content'), filename, {language: 'shell'});
+  const filename = document.querySelector('.hook-filename')!.textContent;
+  createMonaco(document.querySelector<HTMLTextAreaElement>('#content')!, filename, {language: 'shell'});
 }
 
 function initRepoSettingsBranches() {
@@ -82,14 +82,14 @@ function initRepoSettingsBranches() {
 
   for (const el of document.querySelectorAll<HTMLInputElement>('.toggle-target-enabled')) {
     el.addEventListener('change', function () {
-      const target = document.querySelector(this.getAttribute('data-target'));
+      const target = document.querySelector(this.getAttribute('data-target')!);
       target?.classList.toggle('disabled', !this.checked);
     });
   }
 
   for (const el of document.querySelectorAll<HTMLInputElement>('.toggle-target-disabled')) {
     el.addEventListener('change', function () {
-      const target = document.querySelector(this.getAttribute('data-target'));
+      const target = document.querySelector(this.getAttribute('data-target')!);
       if (this.checked) target?.classList.add('disabled'); // only disable, do not auto enable
     });
   }
@@ -100,13 +100,13 @@ function initRepoSettingsBranches() {
 
   // show the `Matched` mark for the status checks that match the pattern
   const markMatchedStatusChecks = () => {
-    const patterns = (document.querySelector<HTMLTextAreaElement>('#status_check_contexts').value || '').split(/[\r\n]+/);
+    const patterns = (document.querySelector<HTMLTextAreaElement>('#status_check_contexts')!.value || '').split(/[\r\n]+/);
     const validPatterns = patterns.map((item) => item.trim()).filter(Boolean as unknown as <T>(x: T | boolean) => x is T);
     const marks = document.querySelectorAll('.status-check-matched-mark');
 
     for (const el of marks) {
       let matched = false;
-      const statusCheck = el.getAttribute('data-status-check');
+      const statusCheck = el.getAttribute('data-status-check')!;
       for (const pattern of validPatterns) {
         if (globMatch(statusCheck, pattern, '/')) {
           matched = true;
@@ -117,7 +117,7 @@ function initRepoSettingsBranches() {
     }
   };
   markMatchedStatusChecks();
-  document.querySelector('#status_check_contexts').addEventListener('input', onInputDebounce(markMatchedStatusChecks));
+  document.querySelector('#status_check_contexts')!.addEventListener('input', onInputDebounce(markMatchedStatusChecks));
 }
 
 function initRepoSettingsOptions() {
@@ -130,17 +130,17 @@ function initRepoSettingsOptions() {
     queryElems(document, selector, (el) => el.classList.toggle('disabled', !enabled));
   };
   queryElems<HTMLInputElement>(pageContent, '.enable-system', (el) => el.addEventListener('change', () => {
-    toggleTargetContextPanel(el.getAttribute('data-target'), el.checked);
-    toggleTargetContextPanel(el.getAttribute('data-context'), !el.checked);
+    toggleTargetContextPanel(el.getAttribute('data-target')!, el.checked);
+    toggleTargetContextPanel(el.getAttribute('data-context')!, !el.checked);
   }));
   queryElems<HTMLInputElement>(pageContent, '.enable-system-radio', (el) => el.addEventListener('change', () => {
-    toggleTargetContextPanel(el.getAttribute('data-target'), el.value === 'true');
-    toggleTargetContextPanel(el.getAttribute('data-context'), el.value === 'false');
+    toggleTargetContextPanel(el.getAttribute('data-target')!, el.value === 'true');
+    toggleTargetContextPanel(el.getAttribute('data-context')!, el.value === 'false');
   }));
 
   queryElems<HTMLInputElement>(pageContent, '.js-tracker-issue-style', (el) => el.addEventListener('change', () => {
     const checkedVal = el.value;
-    pageContent.querySelector('#tracker-issue-style-regex-box').classList.toggle('disabled', checkedVal !== 'regexp');
+    pageContent.querySelector('#tracker-issue-style-regex-box')!.classList.toggle('disabled', checkedVal !== 'regexp');
   }));
 }
 
diff --git a/web_src/js/features/repo-unicode-escape.ts b/web_src/js/features/repo-unicode-escape.ts
index 49e34e22cd..ff3f42095e 100644
--- a/web_src/js/features/repo-unicode-escape.ts
+++ b/web_src/js/features/repo-unicode-escape.ts
@@ -7,8 +7,8 @@ export function initUnicodeEscapeButton() {
 
     const unicodeContentSelector = btn.getAttribute('data-unicode-content-selector');
     const container = unicodeContentSelector ?
-      document.querySelector(unicodeContentSelector) :
-      btn.closest('.file-content, .non-diff-file-content');
+      document.querySelector(unicodeContentSelector)! :
+      btn.closest('.file-content, .non-diff-file-content')!;
     const fileView = container.querySelector('.file-code, .file-view') ?? container;
     if (btn.matches('.escape-button')) {
       fileView.classList.add('unicode-escaped');
diff --git a/web_src/js/features/repo-view-file-tree.ts b/web_src/js/features/repo-view-file-tree.ts
index 98ffdb8a86..8d10cdacb6 100644
--- a/web_src/js/features/repo-view-file-tree.ts
+++ b/web_src/js/features/repo-view-file-tree.ts
@@ -11,8 +11,8 @@ function isUserSignedIn() {
 }
 
 async function toggleSidebar(btn: HTMLElement) {
-  const elToggleShow = document.querySelector('.repo-view-file-tree-toggle[data-toggle-action="show"]');
-  const elFileTreeContainer = document.querySelector('.repo-view-file-tree-container');
+  const elToggleShow = document.querySelector('.repo-view-file-tree-toggle[data-toggle-action="show"]')!;
+  const elFileTreeContainer = document.querySelector('.repo-view-file-tree-container')!;
   const shouldShow = btn.getAttribute('data-toggle-action') === 'show';
   toggleElem(elFileTreeContainer, shouldShow);
   toggleElem(elToggleShow, !shouldShow);
@@ -32,7 +32,7 @@ export async function initRepoViewFileTree() {
 
   registerGlobalEventFunc('click', 'onRepoViewFileTreeToggle', toggleSidebar);
 
-  const fileTree = sidebar.querySelector('#view-file-tree');
+  const fileTree = sidebar.querySelector('#view-file-tree')!;
   createApp(ViewFileTree, {
     repoLink: fileTree.getAttribute('data-repo-link'),
     treePath: fileTree.getAttribute('data-tree-path'),
diff --git a/web_src/js/features/repo-wiki.ts b/web_src/js/features/repo-wiki.ts
index 6ae0947077..950614d57c 100644
--- a/web_src/js/features/repo-wiki.ts
+++ b/web_src/js/features/repo-wiki.ts
@@ -8,8 +8,8 @@ async function initRepoWikiFormEditor() {
   const editArea = document.querySelector<HTMLTextAreaElement>('.repository.wiki .combo-markdown-editor textarea');
   if (!editArea) return;
 
-  const form = document.querySelector('.repository.wiki.new .ui.form');
-  const editorContainer = form.querySelector<HTMLElement>('.combo-markdown-editor');
+  const form = document.querySelector('.repository.wiki.new .ui.form')!;
+  const editorContainer = form.querySelector<HTMLElement>('.combo-markdown-editor')!;
   let editor: ComboMarkdownEditor;
 
   let renderRequesting = false;
diff --git a/web_src/js/features/sshkey-helper.ts b/web_src/js/features/sshkey-helper.ts
index 860bc5b294..519bf582c0 100644
--- a/web_src/js/features/sshkey-helper.ts
+++ b/web_src/js/features/sshkey-helper.ts
@@ -2,7 +2,7 @@ export function initSshKeyFormParser() {
   // Parse SSH Key
   document.querySelector<HTMLTextAreaElement>('#ssh-key-content')?.addEventListener('input', function () {
     const arrays = this.value.split(' ');
-    const title = document.querySelector<HTMLInputElement>('#ssh-key-title');
+    const title = document.querySelector<HTMLInputElement>('#ssh-key-title')!;
     if (!title.value && arrays.length === 3 && arrays[2] !== '') {
       title.value = arrays[2];
     }
diff --git a/web_src/js/features/tablesort.ts b/web_src/js/features/tablesort.ts
index cd77eb971c..f0c57209ea 100644
--- a/web_src/js/features/tablesort.ts
+++ b/web_src/js/features/tablesort.ts
@@ -1,8 +1,8 @@
 export function initTableSort() {
   for (const header of document.querySelectorAll('th[data-sortt-asc]') || []) {
-    const sorttAsc = header.getAttribute('data-sortt-asc');
-    const sorttDesc = header.getAttribute('data-sortt-desc');
-    const sorttDefault = header.getAttribute('data-sortt-default');
+    const sorttAsc = header.getAttribute('data-sortt-asc')!;
+    const sorttDesc = header.getAttribute('data-sortt-desc')!;
+    const sorttDefault = header.getAttribute('data-sortt-default')!;
     header.addEventListener('click', () => {
       tableSort(sorttAsc, sorttDesc, sorttDefault);
     });
diff --git a/web_src/js/features/user-auth-webauthn.ts b/web_src/js/features/user-auth-webauthn.ts
index 1f336b9741..50165c3377 100644
--- a/web_src/js/features/user-auth-webauthn.ts
+++ b/web_src/js/features/user-auth-webauthn.ts
@@ -13,7 +13,7 @@ export async function initUserAuthWebAuthn() {
 
   // webauthn is only supported on secure contexts
   if (!window.isSecureContext) {
-    hideElem(elSignInPasskeyBtn);
+    if (elSignInPasskeyBtn) hideElem(elSignInPasskeyBtn);
     return;
   }
 
@@ -54,7 +54,7 @@ async function loginPasskey() {
     const clientDataJSON = new Uint8Array(credResp.clientDataJSON);
     const rawId = new Uint8Array(credential.rawId);
     const sig = new Uint8Array(credResp.signature);
-    const userHandle = new Uint8Array(credResp.userHandle);
+    const userHandle = new Uint8Array(credResp.userHandle ?? []);
 
     const res = await POST(`${appSubUrl}/user/webauthn/passkey/login`, {
       data: {
@@ -183,7 +183,7 @@ async function webauthnRegistered(newCredential: any) { // TODO: Credential type
 }
 
 function webAuthnError(errorType: string, message:string = '') {
-  const elErrorMsg = document.querySelector(`#webauthn-error-msg`);
+  const elErrorMsg = document.querySelector(`#webauthn-error-msg`)!;
 
   if (errorType === 'general') {
     elErrorMsg.textContent = message || 'unknown error';
@@ -228,7 +228,7 @@ export function initUserAuthWebAuthnRegister() {
 }
 
 async function webAuthnRegisterRequest() {
-  const elNickname = document.querySelector<HTMLInputElement>('#nickname');
+  const elNickname = document.querySelector<HTMLInputElement>('#nickname')!;
 
   const formData = new FormData();
   formData.append('name', elNickname.value);
@@ -246,7 +246,7 @@ async function webAuthnRegisterRequest() {
   }
 
   const options = await res.json();
-  elNickname.closest('div.field').classList.remove('error');
+  elNickname.closest('div.field')!.classList.remove('error');
 
   options.publicKey.challenge = decodeURLEncodedBase64(options.publicKey.challenge);
   options.publicKey.user.id = decodeURLEncodedBase64(options.publicKey.user.id);
diff --git a/web_src/js/features/user-auth.ts b/web_src/js/features/user-auth.ts
index b716287ff2..24c34b4aa5 100644
--- a/web_src/js/features/user-auth.ts
+++ b/web_src/js/features/user-auth.ts
@@ -8,7 +8,7 @@ export function initUserCheckAppUrl() {
 export function initUserAuthOauth2() {
   const outer = document.querySelector('#oauth2-login-navigator');
   if (!outer) return;
-  const inner = document.querySelector('#oauth2-login-navigator-inner');
+  const inner = document.querySelector('#oauth2-login-navigator-inner')!;
 
   checkAppUrl();
 
diff --git a/web_src/js/features/user-settings.ts b/web_src/js/features/user-settings.ts
index 6fbb56e540..ef4d5f25bd 100644
--- a/web_src/js/features/user-settings.ts
+++ b/web_src/js/features/user-settings.ts
@@ -6,9 +6,9 @@ export function initUserSettings() {
   const usernameInput = document.querySelector<HTMLInputElement>('#username');
   if (!usernameInput) return;
   usernameInput.addEventListener('input', function () {
-    const prompt = document.querySelector('#name-change-prompt');
-    const promptRedirect = document.querySelector('#name-change-redirect-prompt');
-    if (this.value.toLowerCase() !== this.getAttribute('data-name').toLowerCase()) {
+    const prompt = document.querySelector('#name-change-prompt')!;
+    const promptRedirect = document.querySelector('#name-change-redirect-prompt')!;
+    if (this.value.toLowerCase() !== this.getAttribute('data-name')!.toLowerCase()) {
       showElem(prompt);
       showElem(promptRedirect);
     } else {
diff --git a/web_src/js/htmx.ts b/web_src/js/htmx.ts
index 9d433dfd57..acc3df1d81 100644
--- a/web_src/js/htmx.ts
+++ b/web_src/js/htmx.ts
@@ -15,12 +15,12 @@ export function initHtmx() {
   // https://htmx.org/events/#htmx:sendError
   document.body.addEventListener('htmx:sendError', (event: Partial<HtmxEvent>) => {
     // TODO: add translations
-    showErrorToast(`Network error when calling ${event.detail.requestConfig.path}`);
+    showErrorToast(`Network error when calling ${event.detail!.requestConfig.path}`);
   });
 
   // https://htmx.org/events/#htmx:responseError
   document.body.addEventListener('htmx:responseError', (event: Partial<HtmxEvent>) => {
     // TODO: add translations
-    showErrorToast(`Error ${event.detail.xhr.status} when calling ${event.detail.requestConfig.path}`);
+    showErrorToast(`Error ${event.detail!.xhr.status} when calling ${event.detail!.requestConfig.path}`);
   });
 }
diff --git a/web_src/js/markup/anchors.ts b/web_src/js/markup/anchors.ts
index a0d49911fe..b5d90e565c 100644
--- a/web_src/js/markup/anchors.ts
+++ b/web_src/js/markup/anchors.ts
@@ -7,7 +7,7 @@ const hasPrefix = (str: string): boolean => str.startsWith('user-content-');
 // scroll to anchor while respecting the `user-content` prefix that exists on the target
 function scrollToAnchor(encodedId?: string): void {
   // FIXME: need to rewrite this function with new a better markup anchor generation logic, too many tricks here
-  let elemId: string;
+  let elemId: string | undefined;
   try {
     elemId = decodeURIComponent(encodedId ?? '');
   } catch {} // ignore the errors, since the "encodedId" is from user's input
@@ -44,7 +44,7 @@ export function initMarkupAnchors(): void {
     // remove `user-content-` prefix from links so they don't show in url bar when clicked
     for (const a of markupEl.querySelectorAll<HTMLAnchorElement>('a[href^="#"]')) {
       const href = a.getAttribute('href');
-      if (!href.startsWith('#user-content-')) continue;
+      if (!href?.startsWith('#user-content-')) continue;
       a.setAttribute('href', `#${removePrefix(href.substring(1))}`);
     }
 
diff --git a/web_src/js/markup/codecopy.ts b/web_src/js/markup/codecopy.ts
index b37aa3a236..a6e07a3cf6 100644
--- a/web_src/js/markup/codecopy.ts
+++ b/web_src/js/markup/codecopy.ts
@@ -17,6 +17,6 @@ export function initMarkupCodeCopy(elMarkup: HTMLElement): void {
     btn.setAttribute('data-clipboard-text', el.textContent.replace(/\r?\n$/, ''));
     // we only want to use `.code-block-container` if it exists, no matter `.code-block` exists or not.
     const btnContainer = el.closest('.code-block-container') ?? el.closest('.code-block');
-    btnContainer.append(btn);
+    btnContainer!.append(btn);
   });
 }
diff --git a/web_src/js/markup/mermaid.ts b/web_src/js/markup/mermaid.ts
index ddd53a7035..e1c2935f23 100644
--- a/web_src/js/markup/mermaid.ts
+++ b/web_src/js/markup/mermaid.ts
@@ -23,7 +23,7 @@ export async function initMarkupCodeMermaid(elMarkup: HTMLElement): Promise<void
     });
 
     const pre = el.closest('pre');
-    if (pre.hasAttribute('data-render-done')) return;
+    if (!pre || pre.hasAttribute('data-render-done')) return;
 
     const source = el.textContent;
     if (mermaidMaxSourceCharacters >= 0 && source.length > mermaidMaxSourceCharacters) {
diff --git a/web_src/js/markup/refissue.ts b/web_src/js/markup/refissue.ts
index 5a05de84fe..30d8924a1d 100644
--- a/web_src/js/markup/refissue.ts
+++ b/web_src/js/markup/refissue.ts
@@ -16,7 +16,7 @@ export function showMarkupRefIssuePopup(e: MouseEvent | FocusEvent) {
   if (getAttachedTippyInstance(refIssue)) return;
   if (refIssue.classList.contains('ref-external-issue')) return;
 
-  const issuePathInfo = parseIssueHref(refIssue.getAttribute('href'));
+  const issuePathInfo = parseIssueHref(refIssue.getAttribute('href')!);
   if (!issuePathInfo.ownerName) return;
 
   const el = document.createElement('div');
diff --git a/web_src/js/markup/render-iframe.ts b/web_src/js/markup/render-iframe.ts
index 842c2be2d6..35649ee2ee 100644
--- a/web_src/js/markup/render-iframe.ts
+++ b/web_src/js/markup/render-iframe.ts
@@ -2,7 +2,7 @@ import {generateElemId, queryElemChildren} from '../utils/dom.ts';
 import {isDarkTheme} from '../utils.ts';
 
 export async function loadRenderIframeContent(iframe: HTMLIFrameElement) {
-  const iframeSrcUrl = iframe.getAttribute('data-src');
+  const iframeSrcUrl = iframe.getAttribute('data-src')!;
   if (!iframe.id) iframe.id = generateElemId('gitea-iframe-');
 
   window.addEventListener('message', (e) => {
diff --git a/web_src/js/markup/tasklist.ts b/web_src/js/markup/tasklist.ts
index dc4bbd9519..7f3417c2bb 100644
--- a/web_src/js/markup/tasklist.ts
+++ b/web_src/js/markup/tasklist.ts
@@ -13,7 +13,7 @@ const preventListener = (e: Event) => e.preventDefault();
 export function initMarkupTasklist(elMarkup: HTMLElement): void {
   if (!elMarkup.matches('[data-can-edit=true]')) return;
 
-  const container = elMarkup.parentNode;
+  const container = elMarkup.parentNode!;
   const checkboxes = elMarkup.querySelectorAll<HTMLInputElement>(`.task-list-item input[type=checkbox]`);
 
   for (const checkbox of checkboxes) {
@@ -24,9 +24,9 @@ export function initMarkupTasklist(elMarkup: HTMLElement): void {
     checkbox.setAttribute('data-editable', 'true');
     checkbox.addEventListener('input', async () => {
       const checkboxCharacter = checkbox.checked ? 'x' : ' ';
-      const position = parseInt(checkbox.getAttribute('data-source-position')) + 1;
+      const position = parseInt(checkbox.getAttribute('data-source-position')!) + 1;
 
-      const rawContent = container.querySelector('.raw-content');
+      const rawContent = container.querySelector('.raw-content')!;
       const oldContent = rawContent.textContent;
 
       const encoder = new TextEncoder();
@@ -53,10 +53,10 @@ export function initMarkupTasklist(elMarkup: HTMLElement): void {
       }
 
       try {
-        const editContentZone = container.querySelector<HTMLDivElement>('.edit-content-zone');
-        const updateUrl = editContentZone.getAttribute('data-update-url');
-        const context = editContentZone.getAttribute('data-context');
-        const contentVersion = editContentZone.getAttribute('data-content-version');
+        const editContentZone = container.querySelector<HTMLDivElement>('.edit-content-zone')!;
+        const updateUrl = editContentZone.getAttribute('data-update-url')!;
+        const context = editContentZone.getAttribute('data-context')!;
+        const contentVersion = editContentZone.getAttribute('data-content-version')!;
 
         const requestBody = new FormData();
         requestBody.append('ignore_attachments', 'true');
diff --git a/web_src/js/modules/diff-file.ts b/web_src/js/modules/diff-file.ts
index f944b8120c..25fc327a54 100644
--- a/web_src/js/modules/diff-file.ts
+++ b/web_src/js/modules/diff-file.ts
@@ -12,7 +12,7 @@ export type DiffTreeEntry = {
   DiffStatus: DiffStatus,
   EntryMode: string,
   IsViewed: boolean,
-  Children: DiffTreeEntry[],
+  Children: DiffTreeEntry[] | null,
   FileIcon: string,
   ParentEntry?: DiffTreeEntry,
 };
@@ -25,7 +25,7 @@ type DiffFileTree = {
   folderIcon: string;
   folderOpenIcon: string;
   diffFileTree: DiffFileTreeData;
-  fullNameMap?: Record<string, DiffTreeEntry>
+  fullNameMap: Record<string, DiffTreeEntry>
   fileTreeIsVisible: boolean;
   selectedItem: string;
 };
diff --git a/web_src/js/modules/fetch.ts b/web_src/js/modules/fetch.ts
index 0c078bfe78..14e7954116 100644
--- a/web_src/js/modules/fetch.ts
+++ b/web_src/js/modules/fetch.ts
@@ -10,8 +10,8 @@ const safeMethods = new Set(['GET', 'HEAD', 'OPTIONS', 'TRACE']);
 // which will automatically set an appropriate headers. For json content, only object
 // and array types are currently supported.
 export function request(url: string, {method = 'GET', data, headers = {}, ...other}: RequestOpts = {}): Promise<Response> {
-  let body: string | FormData | URLSearchParams;
-  let contentType: string;
+  let body: string | FormData | URLSearchParams | undefined;
+  let contentType: string | undefined;
   if (data instanceof FormData || data instanceof URLSearchParams) {
     body = data;
   } else if (isObject(data) || Array.isArray(data)) {
diff --git a/web_src/js/modules/fomantic/tab.ts b/web_src/js/modules/fomantic/tab.ts
index ceae9dd098..b9578c9637 100644
--- a/web_src/js/modules/fomantic/tab.ts
+++ b/web_src/js/modules/fomantic/tab.ts
@@ -7,7 +7,7 @@ export function initFomanticTab() {
       const tabName = elBtn.getAttribute('data-tab');
       if (!tabName) continue;
       elBtn.addEventListener('click', () => {
-        const elTab = document.querySelector(`.ui.tab[data-tab="${tabName}"]`);
+        const elTab = document.querySelector(`.ui.tab[data-tab="${tabName}"]`)!;
         queryElemSiblings(elTab, `.ui.tab`, (el) => el.classList.remove('active'));
         queryElemSiblings(elBtn, `[data-tab]`, (el) => el.classList.remove('active'));
         elBtn.classList.add('active');
diff --git a/web_src/js/modules/observer.ts b/web_src/js/modules/observer.ts
index 47c276c866..1bbf304b27 100644
--- a/web_src/js/modules/observer.ts
+++ b/web_src/js/modules/observer.ts
@@ -42,7 +42,7 @@ export function registerGlobalInitFunc<T extends HTMLElement>(name: string, hand
 }
 
 function callGlobalInitFunc(el: HTMLElement) {
-  const initFunc = el.getAttribute('data-global-init');
+  const initFunc = el.getAttribute('data-global-init')!;
   const func = globalInitFuncs[initFunc];
   if (!func) throw new Error(`Global init function "${initFunc}" not found`);
 
@@ -66,7 +66,7 @@ function attachGlobalEvents() {
   });
 }
 
-export function initGlobalSelectorObserver(perfTracer?: InitPerformanceTracer): void {
+export function initGlobalSelectorObserver(perfTracer: InitPerformanceTracer | null): void {
   if (globalSelectorObserverInited) throw new Error('initGlobalSelectorObserver() already called');
   globalSelectorObserverInited = true;
 
diff --git a/web_src/js/modules/sortable.ts b/web_src/js/modules/sortable.ts
index b700633cbb..d03871bb04 100644
--- a/web_src/js/modules/sortable.ts
+++ b/web_src/js/modules/sortable.ts
@@ -9,12 +9,12 @@ export async function createSortable(el: Element, opts: {handle?: string} & Sort
     animation: 150,
     ghostClass: 'card-ghost',
     onChoose: (e: SortableEvent) => {
-      const handle = opts.handle ? e.item.querySelector(opts.handle) : e.item;
+      const handle = opts.handle ? e.item.querySelector(opts.handle)! : e.item;
       handle.classList.add('tw-cursor-grabbing');
       opts.onChoose?.(e);
     },
     onUnchoose: (e: SortableEvent) => {
-      const handle = opts.handle ? e.item.querySelector(opts.handle) : e.item;
+      const handle = opts.handle ? e.item.querySelector(opts.handle)! : e.item;
       handle.classList.remove('tw-cursor-grabbing');
       opts.onUnchoose?.(e);
     },
diff --git a/web_src/js/modules/tippy.ts b/web_src/js/modules/tippy.ts
index 6f42a4f987..d616216ab5 100644
--- a/web_src/js/modules/tippy.ts
+++ b/web_src/js/modules/tippy.ts
@@ -68,7 +68,7 @@ export function createTippy(target: Element, opts: TippyOpts = {}): Instance {
  *
  * Note: "tooltip" doesn't equal to "tippy". "tooltip" means a auto-popup content, it just uses tippy as the implementation.
  */
-function attachTooltip(target: Element, content: Content = null): Instance {
+function attachTooltip(target: Element, content: Content | null = null): Instance | null {
   switchTitleToTooltip(target);
 
   content = content ?? target.getAttribute('data-tooltip-content');
@@ -125,7 +125,7 @@ function switchTitleToTooltip(target: Element): void {
  * The tippy by default uses "mouseenter" event to show, so we use "mouseover" event to switch to tippy
  */
 function lazyTooltipOnMouseHover(this: HTMLElement, e: Event): void {
-  e.target.removeEventListener('mouseover', lazyTooltipOnMouseHover, true);
+  (e.target as HTMLElement).removeEventListener('mouseover', lazyTooltipOnMouseHover, true);
   attachTooltip(this);
 }
 
@@ -184,7 +184,7 @@ export function initGlobalTooltips(): void {
 export function showTemporaryTooltip(target: Element, content: Content): void {
   // if the target is inside a dropdown or tippy popup, the menu will be hidden soon
   // so display the tooltip on the "aria-controls" element or dropdown instead
-  let refClientRect: DOMRect;
+  let refClientRect: DOMRect | undefined;
   const popupTippyId = target.closest(`[data-tippy-root]`)?.id;
   if (popupTippyId) {
     // for example, the "Copy Permalink" button in the "File View" page for the selected lines
diff --git a/web_src/js/modules/toast.ts b/web_src/js/modules/toast.ts
index 395f31bc82..c551381bab 100644
--- a/web_src/js/modules/toast.ts
+++ b/web_src/js/modules/toast.ts
@@ -52,7 +52,7 @@ function showToast(message: string, level: Intent, {gravity, position, duration,
   if (preventDuplicates) {
     const toastEl = parent.querySelector(`:scope > .toastify.on[data-toast-unique-key="${CSS.escape(duplicateKey)}"]`);
     if (toastEl) {
-      const toastDupNumEl = toastEl.querySelector('.toast-duplicate-number');
+      const toastDupNumEl = toastEl.querySelector('.toast-duplicate-number')!;
       showElem(toastDupNumEl);
       toastDupNumEl.textContent = String(Number(toastDupNumEl.textContent) + 1);
       animateOnce(toastDupNumEl, 'pulse-1p5-200');
@@ -77,9 +77,10 @@ function showToast(message: string, level: Intent, {gravity, position, duration,
   });
 
   toast.showToast();
-  toast.toastElement.querySelector('.toast-close').addEventListener('click', () => toast.hideToast());
-  toast.toastElement.setAttribute('data-toast-unique-key', duplicateKey);
-  (toast.toastElement as ToastifyElement)._giteaToastifyInstance = toast;
+  const el = toast.toastElement as ToastifyElement;
+  el.querySelector('.toast-close')!.addEventListener('click', () => toast.hideToast());
+  el.setAttribute('data-toast-unique-key', duplicateKey);
+  el._giteaToastifyInstance = toast;
   return toast;
 }
 
diff --git a/web_src/js/standalone/devtest.ts b/web_src/js/standalone/devtest.ts
index faa38dc467..39c41db042 100644
--- a/web_src/js/standalone/devtest.ts
+++ b/web_src/js/standalone/devtest.ts
@@ -1,11 +1,13 @@
-import {showInfoToast, showWarningToast, showErrorToast} from '../modules/toast.ts';
+import {showInfoToast, showWarningToast, showErrorToast, type Toast} from '../modules/toast.ts';
+
+type LevelMap = Record<string, (message: string) => Toast | null>;
 
 function initDevtestToast() {
-  const levelMap: Record<string, any> = {info: showInfoToast, warning: showWarningToast, error: showErrorToast};
+  const levelMap: LevelMap = {info: showInfoToast, warning: showWarningToast, error: showErrorToast};
   for (const el of document.querySelectorAll('.toast-test-button')) {
     el.addEventListener('click', () => {
-      const level = el.getAttribute('data-toast-level');
-      const message = el.getAttribute('data-toast-message');
+      const level = el.getAttribute('data-toast-level')!;
+      const message = el.getAttribute('data-toast-message')!;
       levelMap[level](message);
     });
   }
diff --git a/web_src/js/standalone/external-render-iframe.ts b/web_src/js/standalone/external-render-iframe.ts
index 3abf128bc3..8776710cda 100644
--- a/web_src/js/standalone/external-render-iframe.ts
+++ b/web_src/js/standalone/external-render-iframe.ts
@@ -35,7 +35,7 @@ function mainExternalRenderIframe() {
     // safe links: "./any", "../any", "/any", "//host/any", "http://host/any", "https://host/any"
     if (href.startsWith('.') || href.startsWith('/') || href.startsWith('http://') || href.startsWith('https://')) {
       e.preventDefault();
-      openIframeLink(href, el.getAttribute('target'));
+      openIframeLink(href, el.getAttribute('target')!);
     }
   });
 }
diff --git a/web_src/js/standalone/swagger.ts b/web_src/js/standalone/swagger.ts
index 4b17ba21a8..62d1a56306 100644
--- a/web_src/js/standalone/swagger.ts
+++ b/web_src/js/standalone/swagger.ts
@@ -2,7 +2,7 @@ import SwaggerUI from 'swagger-ui-dist/swagger-ui-es-bundle.js';
 import 'swagger-ui-dist/swagger-ui.css';
 
 window.addEventListener('load', async () => {
-  const url = document.querySelector('#swagger-ui').getAttribute('data-source');
+  const url = document.querySelector('#swagger-ui')!.getAttribute('data-source')!;
   const res = await fetch(url);
   const spec = await res.json();
 
diff --git a/web_src/js/types.ts b/web_src/js/types.ts
index 31f41766e7..2f76a58c9d 100644
--- a/web_src/js/types.ts
+++ b/web_src/js/types.ts
@@ -41,7 +41,7 @@ export type IssuePathInfo = {
   ownerName: string,
   repoName: string,
   pathType: string,
-  indexString?: string,
+  indexString: string,
 };
 
 export type IssuePageInfo = {
diff --git a/web_src/js/utils.ts b/web_src/js/utils.ts
index c3db28c0e2..afe8c8f472 100644
--- a/web_src/js/utils.ts
+++ b/web_src/js/utils.ts
@@ -23,7 +23,7 @@ export function extname(path: string): string {
 }
 
 /** test whether a variable is an object */
-export function isObject(obj: any): boolean {
+export function isObject<T = Record<string, any>>(obj: any): obj is T {
   return Object.prototype.toString.call(obj) === '[object Object]';
 }
 
@@ -60,9 +60,9 @@ export function parseRepoOwnerPathInfo(pathname: string): RepoOwnerPathInfo {
 export function parseIssuePageInfo(): IssuePageInfo {
   const el = document.querySelector('#issue-page-info');
   return {
-    issueNumber: parseInt(el?.getAttribute('data-issue-index')),
+    issueNumber: parseInt(el?.getAttribute('data-issue-index') || ''),
     issueDependencySearchType: el?.getAttribute('data-issue-dependency-search-type') || '',
-    repoId: parseInt(el?.getAttribute('data-issue-repo-id')),
+    repoId: parseInt(el?.getAttribute('data-issue-repo-id') || ''),
     repoLink: el?.getAttribute('data-issue-repo-link') || '',
   };
 }
@@ -93,10 +93,14 @@ export function blobToDataURI(blob: Blob): Promise<string> {
     try {
       const reader = new FileReader();
       reader.addEventListener('load', (e) => {
-        resolve(e.target.result as string);
+        if (e.target) {
+          resolve(e.target.result as string);
+        } else {
+          reject(new Error('blobToDataURI: FileReader failed'));
+        }
       });
       reader.addEventListener('error', () => {
-        reject(new Error('FileReader failed'));
+        reject(new Error('blobToDataURI: FileReader error'));
       });
       reader.readAsDataURL(blob);
     } catch (err) {
@@ -116,9 +120,10 @@ export function convertImage(blob: Blob, mime: string): Promise<Blob> {
           canvas.width = img.naturalWidth;
           canvas.height = img.naturalHeight;
           const context = canvas.getContext('2d');
+          if (!context) return reject(new Error('convertImage: no context'));
           context.drawImage(img, 0, 0);
           canvas.toBlob((blob) => {
-            if (!(blob instanceof Blob)) return reject(new Error('imageBlobToPng failed'));
+            if (!(blob instanceof Blob)) return reject(new Error('convertImage: toBlob failed'));
             resolve(blob);
           }, mime);
         } catch (err) {
@@ -126,7 +131,7 @@ export function convertImage(blob: Blob, mime: string): Promise<Blob> {
         }
       });
       img.addEventListener('error', () => {
-        reject(new Error('imageBlobToPng failed'));
+        reject(new Error('convertImage: image failed to load'));
       });
       img.src = await blobToDataURI(blob);
     } catch (err) {
@@ -179,26 +184,25 @@ export function sleep(ms: number): Promise<void> {
 }
 
 export function isImageFile({name, type}: {name?: string, type?: string}): boolean {
-  return /\.(avif|jpe?g|png|gif|webp|svg|heic)$/i.test(name || '') || type?.startsWith('image/');
+  return Boolean(/\.(avif|jpe?g|png|gif|webp|svg|heic)$/i.test(name || '') || type?.startsWith('image/'));
 }
 
 export function isVideoFile({name, type}: {name?: string, type?: string}): boolean {
-  return /\.(mpe?g|mp4|mkv|webm)$/i.test(name || '') || type?.startsWith('video/');
+  return Boolean(/\.(mpe?g|mp4|mkv|webm)$/i.test(name || '') || type?.startsWith('video/'));
 }
 
 export function toggleFullScreen(fullscreenElementsSelector: string, isFullScreen: boolean, sourceParentSelector?: string): void {
   // hide other elements
-  const headerEl = document.querySelector('#navbar');
-  const contentEl = document.querySelector('.page-content');
-  const footerEl = document.querySelector('.page-footer');
+  const headerEl = document.querySelector('#navbar')!;
+  const contentEl = document.querySelector('.page-content')!;
+  const footerEl = document.querySelector('.page-footer')!;
   toggleElem(headerEl, !isFullScreen);
   toggleElem(contentEl, !isFullScreen);
   toggleElem(footerEl, !isFullScreen);
 
-  const sourceParentEl = sourceParentSelector ? document.querySelector(sourceParentSelector) : contentEl;
-
-  const fullScreenEl = document.querySelector(fullscreenElementsSelector);
-  const outerEl = document.querySelector('.full.height');
+  const sourceParentEl = sourceParentSelector ? document.querySelector(sourceParentSelector)! : contentEl;
+  const fullScreenEl = document.querySelector(fullscreenElementsSelector)!;
+  const outerEl = document.querySelector('.full.height')!;
   toggleElemClass(fullscreenElementsSelector, 'fullscreen', isFullScreen);
   if (isFullScreen) {
     outerEl.append(fullScreenEl);
diff --git a/web_src/js/utils/dom.test.ts b/web_src/js/utils/dom.test.ts
index 057ea9808c..15cde00ae4 100644
--- a/web_src/js/utils/dom.test.ts
+++ b/web_src/js/utils/dom.test.ts
@@ -28,11 +28,11 @@ test('querySingleVisibleElem', () => {
   let el = createElementFromHTML('<div></div>');
   expect(querySingleVisibleElem(el, 'span')).toBeNull();
   el = createElementFromHTML('<div><span>foo</span></div>');
-  expect(querySingleVisibleElem(el, 'span').textContent).toEqual('foo');
+  expect(querySingleVisibleElem(el, 'span')!.textContent).toEqual('foo');
   el = createElementFromHTML('<div><span style="display: none;">foo</span><span>bar</span></div>');
-  expect(querySingleVisibleElem(el, 'span').textContent).toEqual('bar');
+  expect(querySingleVisibleElem(el, 'span')!.textContent).toEqual('bar');
   el = createElementFromHTML('<div><span class="some-class tw-hidden">foo</span><span>bar</span></div>');
-  expect(querySingleVisibleElem(el, 'span').textContent).toEqual('bar');
+  expect(querySingleVisibleElem(el, 'span')!.textContent).toEqual('bar');
   el = createElementFromHTML('<div><span>foo</span><span>bar</span></div>');
   expect(() => querySingleVisibleElem(el, 'span')).toThrowError('Expected exactly one visible element');
 });
diff --git a/web_src/js/utils/dom.ts b/web_src/js/utils/dom.ts
index 3a1b74c1db..dc504b7056 100644
--- a/web_src/js/utils/dom.ts
+++ b/web_src/js/utils/dom.ts
@@ -7,7 +7,6 @@ type ArrayLikeIterable<T> = ArrayLike<T> & Iterable<T>; // for NodeListOf and Ar
 type ElementArg = Element | string | ArrayLikeIterable<Element> | ReturnType<typeof $>;
 type ElementsCallback<T extends Element> = (el: T) => Promisable<any>;
 type ElementsCallbackWithArgs = (el: Element, ...args: any[]) => Promisable<any>;
-export type DOMEvent<E extends Event, T extends Element = HTMLElement> = E & {target: Partial<T>;};
 
 function elementsCall(el: ElementArg, func: ElementsCallbackWithArgs, ...args: any[]): ArrayLikeIterable<Element> {
   if (typeof el === 'string' || el instanceof String) {
@@ -65,6 +64,7 @@ function applyElemsCallback<T extends Element>(elems: ArrayLikeIterable<T>, fn?:
 }
 
 export function queryElemSiblings<T extends Element>(el: Element, selector = '*', fn?: ElementsCallback<T>): ArrayLikeIterable<T> {
+  if (!el.parentNode) return [];
   const elems = Array.from(el.parentNode.children) as T[];
   return applyElemsCallback<T>(elems.filter((child: Element) => {
     return child !== el && child.matches(selector);
@@ -125,10 +125,10 @@ export function isDocumentFragmentOrElementNode(el: Node) {
 export function autosize(textarea: HTMLTextAreaElement, {viewportMarginBottom = 0}: {viewportMarginBottom?: number} = {}) {
   let isUserResized = false;
   // lastStyleHeight and initialStyleHeight are CSS values like '100px'
-  let lastMouseX: number;
-  let lastMouseY: number;
-  let lastStyleHeight: string;
-  let initialStyleHeight: string;
+  let lastMouseX: number | undefined;
+  let lastMouseY: number | undefined;
+  let lastStyleHeight: string | undefined;
+  let initialStyleHeight: string | undefined;
 
   function onUserResize(event: MouseEvent) {
     if (isUserResized) return;
@@ -153,7 +153,8 @@ export function autosize(textarea: HTMLTextAreaElement, {viewportMarginBottom =
       el = el.offsetParent as HTMLTextAreaElement;
     }
 
-    const top = offsetTop - document.defaultView.scrollY;
+    const scrollY = document.defaultView ? document.defaultView.scrollY : 0;
+    const top = offsetTop - scrollY;
     const bottom = document.documentElement.clientHeight - (top + textarea.offsetHeight);
     return {top, bottom};
   }
@@ -265,10 +266,10 @@ export function submitEventSubmitter(e: any) {
   return needSubmitEventPolyfill ? (e.target._submitter || null) : e.submitter;
 }
 
-function submitEventPolyfillListener(e: DOMEvent<Event>) {
-  const form = e.target.closest('form');
+function submitEventPolyfillListener(e: Event) {
+  const form = (e.target as HTMLElement).closest('form');
   if (!form) return;
-  form._submitter = e.target.closest('button:not([type]), button[type="submit"], input[type="submit"]');
+  form._submitter = (e.target as HTMLElement).closest('button:not([type]), button[type="submit"], input[type="submit"]');
 }
 
 export function initSubmitEventPolyfill() {
@@ -283,7 +284,7 @@ export function isElemVisible(el: HTMLElement): boolean {
   // This function DOESN'T account for all possible visibility scenarios, its behavior is covered by the tests of "querySingleVisibleElem"
   if (!el) return false;
   // checking el.style.display is not necessary for browsers, but it is required by some tests with happy-dom because happy-dom doesn't really do layout
-  return !el.classList.contains('tw-hidden') && (el.offsetWidth || el.offsetHeight || el.getClientRects().length) && el.style.display !== 'none';
+  return Boolean(!el.classList.contains('tw-hidden') && (el.offsetWidth || el.offsetHeight || el.getClientRects().length) && el.style.display !== 'none');
 }
 
 export function createElementFromHTML<T extends HTMLElement>(htmlString: string): T {
@@ -293,14 +294,14 @@ export function createElementFromHTML<T extends HTMLElement>(htmlString: string)
   if (htmlString.startsWith('<tr')) {
     const container = document.createElement('table');
     container.innerHTML = htmlString;
-    return container.querySelector<T>('tr');
+    return container.querySelector<T>('tr')!;
   }
   const div = document.createElement('div');
   div.innerHTML = htmlString;
   return div.firstChild as T;
 }
 
-export function createElementFromAttrs(tagName: string, attrs: Record<string, any>, ...children: (Node | string)[]): HTMLElement {
+export function createElementFromAttrs(tagName: string, attrs: Record<string, any> | null, ...children: (Node | string)[]): HTMLElement {
   const el = document.createElement(tagName);
   for (const [key, value] of Object.entries(attrs || {})) {
     if (value === undefined || value === null) continue;
diff --git a/web_src/js/webcomponents/absolute-date.ts b/web_src/js/webcomponents/absolute-date.ts
index 23a8606673..5ab4deaa14 100644
--- a/web_src/js/webcomponents/absolute-date.ts
+++ b/web_src/js/webcomponents/absolute-date.ts
@@ -15,15 +15,17 @@ window.customElements.define('absolute-date', class extends HTMLElement {
   initialized = false;
 
   update = () => {
-    const opt: Record<string, string> = {};
+    const opts: Record<string, string> = {};
     for (const attr of ['year', 'month', 'weekday', 'day']) {
-      if (this.getAttribute(attr)) opt[attr] = this.getAttribute(attr);
+      if (this.getAttribute(attr)) {
+        opts[attr] = this.getAttribute(attr)!;
+      }
     }
     const lang = this.closest('[lang]')?.getAttribute('lang') ||
       this.ownerDocument.documentElement.getAttribute('lang') || '';
 
     if (!this.shadowRoot) this.attachShadow({mode: 'open'});
-    this.shadowRoot.textContent = toAbsoluteLocaleDate(this.getAttribute('date'), lang, opt);
+    this.shadowRoot!.textContent = toAbsoluteLocaleDate(this.getAttribute('date')!, lang, opts);
   };
 
   attributeChangedCallback(_name: string, oldValue: string | null, newValue: string | null) {
diff --git a/web_src/js/webcomponents/origin-url.ts b/web_src/js/webcomponents/origin-url.ts
index dbb910ce6c..e39d3ad713 100644
--- a/web_src/js/webcomponents/origin-url.ts
+++ b/web_src/js/webcomponents/origin-url.ts
@@ -2,6 +2,6 @@ import {toOriginUrl} from '../utils/url.ts';
 
 window.customElements.define('origin-url', class extends HTMLElement {
   connectedCallback() {
-    this.textContent = toOriginUrl(this.getAttribute('data-url'));
+    this.textContent = toOriginUrl(this.getAttribute('data-url')!);
   }
 });
diff --git a/web_src/js/webcomponents/overflow-menu.ts b/web_src/js/webcomponents/overflow-menu.ts
index ae93f2b758..b1294eae3a 100644
--- a/web_src/js/webcomponents/overflow-menu.ts
+++ b/web_src/js/webcomponents/overflow-menu.ts
@@ -6,7 +6,7 @@ import octiconKebabHorizontal from '../../../public/assets/img/svg/octicon-kebab
 window.customElements.define('overflow-menu', class extends HTMLElement {
   tippyContent: HTMLDivElement;
   tippyItems: Array<HTMLElement>;
-  button: HTMLButtonElement;
+  button: HTMLButtonElement | null;
   menuItemsEl: HTMLElement;
   resizeObserver: ResizeObserver;
   mutationObserver: MutationObserver;
@@ -38,8 +38,8 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
         } else if (e.key === 'Escape') {
           e.preventDefault();
           e.stopPropagation();
-          this.button._tippy.hide();
-          this.button.focus();
+          this.button?._tippy.hide();
+          this.button?.focus();
         } else if (e.key === ' ' || e.code === 'Enter') {
           if (document.activeElement?.matches('[role="menuitem"]')) {
             e.preventDefault();
@@ -50,7 +50,7 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
           if (document.activeElement?.matches('.tippy-target')) {
             e.preventDefault();
             e.stopPropagation();
-            document.activeElement.querySelector<HTMLElement>('[role="menuitem"]:first-of-type').focus();
+            document.activeElement.querySelector<HTMLElement>('[role="menuitem"]:first-of-type')?.focus();
           } else if (document.activeElement?.matches('[role="menuitem"]')) {
             e.preventDefault();
             e.stopPropagation();
@@ -60,7 +60,7 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
           if (document.activeElement?.matches('.tippy-target')) {
             e.preventDefault();
             e.stopPropagation();
-            document.activeElement.querySelector<HTMLElement>('[role="menuitem"]:last-of-type').focus();
+            document.activeElement.querySelector<HTMLElement>('[role="menuitem"]:last-of-type')?.focus();
           } else if (document.activeElement?.matches('[role="menuitem"]')) {
             e.preventDefault();
             e.stopPropagation();
@@ -170,7 +170,7 @@ window.customElements.define('overflow-menu', class extends HTMLElement {
       for (const item of this.querySelectorAll('.item')) {
         for (const child of item.childNodes) {
           if (child.nodeType === Node.TEXT_NODE) {
-            const text = child.textContent.trim(); // whitespace is insignificant inside flexbox
+            const text = child.textContent?.trim(); // whitespace is insignificant inside flexbox
             if (!text) continue;
             const span = document.createElement('span');
             span.classList.add('resize-for-semibold');