Improve html escape (#34911)

drop "escape-goat"

.eslintrc.cjs

@@ -91,6 +91,7 @@ module.exports = {
       plugins: ['@vitest/eslint-plugin'],
       globals: vitestPlugin.environments.env.globals,
       rules: {
+        'github/unescaped-html-literal': [0],
         '@vitest/consistent-test-filename': [0],
         '@vitest/consistent-test-it': [0],
         '@vitest/expect-expect': [0],
@@ -423,7 +424,7 @@ module.exports = {
     'github/no-useless-passive': [2],
     'github/prefer-observers': [2],
     'github/require-passive-events': [2],
-    'github/unescaped-html-literal': [0],
+    'github/unescaped-html-literal': [2],
     'grouped-accessor-pairs': [2],
     'guard-for-in': [0],
     'id-blacklist': [0],

package-lock.json

@@ -28,7 +28,6 @@
         "dropzone": "6.0.0-beta.2",
         "easymde": "2.20.0",
         "esbuild-loader": "4.3.0",
-        "escape-goat": "4.0.0",
         "fast-glob": "3.3.3",
         "htmx.org": "2.0.6",
         "idiomorph": "0.7.3",
@@ -6563,18 +6562,6 @@
         "node": ">=6"
       }
     },
-    "node_modules/escape-goat": {
-      "version": "4.0.0",
-      "resolved": "https://registry.npmjs.org/escape-goat/-/escape-goat-4.0.0.tgz",
-      "integrity": "sha512-2Sd4ShcWxbx6OY1IHyla/CVNwvg7XwZVoXZHcSu9w9SReNP1EzzD5T8NWKIR38fIqEns9kDWKUQTXXAmlDrdPg==",
-      "license": "MIT",
-      "engines": {
-        "node": ">=12"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
-      }
-    },
     "node_modules/escape-string-regexp": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/escape-string-regexp/-/escape-string-regexp-4.0.0.tgz",

package.json

@@ -27,7 +27,6 @@
     "dropzone": "6.0.0-beta.2",
     "easymde": "2.20.0",
     "esbuild-loader": "4.3.0",
-    "escape-goat": "4.0.0",
     "fast-glob": "3.3.3",
     "htmx.org": "2.0.6",
     "idiomorph": "0.7.3",

web_src/js/bootstrap.ts

@@ -2,6 +2,7 @@
 // to make sure the error handler always works, we should never import `window.config`, because
 // some user's custom template breaks it.
 import type {Intent} from './types.ts';
+import {html} from './utils/html.ts';
 
 // This sets up the URL prefix used in webpack's chunk loading.
 // This file must be imported before any lazy-loading is being attempted.
@@ -23,7 +24,7 @@ export function showGlobalErrorMessage(msg: string, msgType: Intent = 'error') {
   let msgDiv = msgContainer.querySelector<HTMLDivElement>(`.js-global-error[data-global-error-msg-compact="${msgCompact}"]`);
   if (!msgDiv) {
     const el = document.createElement('div');
-    el.innerHTML = `<div class="ui container js-global-error tw-my-[--page-spacing]"><div class="ui ${msgType} message tw-text-center tw-whitespace-pre-line"></div></div>`;
+    el.innerHTML = html`<div class="ui container js-global-error tw-my-[--page-spacing]"><div class="ui ${msgType} message tw-text-center tw-whitespace-pre-line"></div></div>`;
     msgDiv = el.childNodes[0] as HTMLDivElement;
   }
   // merge duplicated messages into "the message (count)" format

web_src/js/components/ViewFileTreeStore.ts

@@ -2,6 +2,7 @@ import {reactive} from 'vue';
 import {GET} from '../modules/fetch.ts';
 import {pathEscapeSegments} from '../utils/url.ts';
 import {createElementFromHTML} from '../utils/dom.ts';
+import {html} from '../utils/html.ts';
 
 export function createViewFileTreeStore(props: { repoLink: string, treePath: string, currentRefNameSubURL: string}) {
   const store = reactive({
@@ -16,7 +17,7 @@ export function createViewFileTreeStore(props: { repoLink: string, treePath: str
         if (!document.querySelector(`.global-svg-icon-pool #${svgId}`)) poolSvgs.push(svgContent);
       }
       if (poolSvgs.length) {
-        const svgContainer = createElementFromHTML('<div class="global-svg-icon-pool tw-hidden"></div>');
+        const svgContainer = createElementFromHTML(html`<div class="global-svg-icon-pool tw-hidden"></div>`);
         svgContainer.innerHTML = poolSvgs.join('');
         document.body.append(svgContainer);
       }

web_src/js/features/comp/ConfirmModal.ts

@@ -1,5 +1,5 @@
 import {svg} from '../../svg.ts';
-import {htmlEscape} from 'escape-goat';
+import {html, htmlRaw} from '../../utils/html.ts';
 import {createElementFromHTML} from '../../utils/dom.ts';
 import {fomanticQuery} from '../../modules/fomantic/base.ts';
 
@@ -12,17 +12,17 @@ type ConfirmModalOptions = {
 }
 
 export function createConfirmModal({header = '', content = '', confirmButtonColor = 'primary'}:ConfirmModalOptions = {}): HTMLElement {
-  const headerHtml = header ? `<div class="header">${htmlEscape(header)}</div>` : '';
+  const headerHtml = header ? html`<div class="header">${header}</div>` : '';
-  return createElementFromHTML(`
+  return createElementFromHTML(html`
     <div class="ui g-modal-confirm modal">
-  ${headerHtml}
+      ${htmlRaw(headerHtml)}
-  <div class="content">${htmlEscape(content)}</div>
+      <div class="content">${content}</div>
       <div class="actions">
-    <button class="ui cancel button">${svg('octicon-x')} ${htmlEscape(i18n.modal_cancel)}</button>
+        <button class="ui cancel button">${htmlRaw(svg('octicon-x'))} ${i18n.modal_cancel}</button>
-    <button class="ui ${confirmButtonColor} ok button">${svg('octicon-check')} ${htmlEscape(i18n.modal_confirm)}</button>
+        <button class="ui ${confirmButtonColor} ok button">${htmlRaw(svg('octicon-check'))} ${i18n.modal_confirm}</button>
       </div>
     </div>
-`);
+  `.trim());
 }
 
 export function confirmModal(modal: HTMLElement | ConfirmModalOptions): Promise<boolean> {

web_src/js/features/comp/EditorUpload.ts

@@ -114,7 +114,7 @@ async function handleUploadFiles(editor: CodeMirrorEditor | TextareaEditor, drop
 
 export function removeAttachmentLinksFromMarkdown(text: string, fileUuid: string) {
   text = text.replace(new RegExp(`!?\\[([^\\]]+)\\]\\(/?attachments/${fileUuid}\\)`, 'g'), '');
-  text = text.replace(new RegExp(`<img[^>]+src="/?attachments/${fileUuid}"[^>]*>`, 'g'), '');
+  text = text.replace(new RegExp(`[<]img[^>]+src="/?attachments/${fileUuid}"[^>]*>`, 'g'), '');
   return text;
 }
 

web_src/js/features/comp/SearchUserBox.ts

@@ -1,4 +1,4 @@
-import {htmlEscape} from 'escape-goat';
+import {htmlEscape} from '../../utils/html.ts';
 import {fomanticQuery} from '../../modules/fomantic/base.ts';
 
 const {appSubUrl} = window.config;

web_src/js/features/dropzone.ts

@@ -1,5 +1,5 @@
 import {svg} from '../svg.ts';
-import {htmlEscape} from 'escape-goat';
+import {html} from '../utils/html.ts';
 import {clippie} from 'clippie';
 import {showTemporaryTooltip} from '../modules/tippy.ts';
 import {GET, POST} from '../modules/fetch.ts';
@@ -33,14 +33,14 @@ export function generateMarkdownLinkForAttachment(file: Partial<CustomDropzoneFi
       // 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}"
-      fileMarkdown = `<img width="${Math.round(width / dppx)}" alt="${htmlEscape(file.name)}" src="attachments/${htmlEscape(file.uuid)}">`;
+      fileMarkdown = html`<img width="${Math.round(width / dppx)}" alt="${file.name}" src="attachments/${file.uuid}">`;
     } else {
       // Markdown always renders the image with a relative path, so the final URL is "/sub-path/owner/repo/attachments/{uuid}"
       // TODO: it should also use relative path for consistency, because absolute is ambiguous for "/sub-path/attachments" or "/attachments"
       fileMarkdown = `![${file.name}](/attachments/${file.uuid})`;
     }
   } else if (isVideoFile(file)) {
-    fileMarkdown = `<video src="attachments/${htmlEscape(file.uuid)}" title="${htmlEscape(file.name)}" controls></video>`;
+    fileMarkdown = html`<video src="attachments/${file.uuid}" title="${file.name}" controls></video>`;
   }
   return fileMarkdown;
 }

web_src/js/features/emoji.ts

@@ -1,4 +1,5 @@
 import emojis from '../../../assets/emoji.json' with {type: 'json'};
+import {html} from '../utils/html.ts';
 
 const {assetUrlPrefix, customEmojis} = window.config;
 
@@ -24,12 +25,11 @@ for (const key of emojiKeys) {
 export function emojiHTML(name: string) {
   let inner;
   if (Object.hasOwn(customEmojis, name)) {
-    inner = `<img alt=":${name}:" src="${assetUrlPrefix}/img/emoji/${name}.png">`;
+    inner = html`<img alt=":${name}:" src="${assetUrlPrefix}/img/emoji/${name}.png">`;
   } else {
     inner = emojiString(name);
   }
-
+  return html`<span class="emoji" title=":${name}:">${inner}</span>`;
-  return `<span class="emoji" title=":${name}:">${inner}</span>`;
 }
 
 // retrieve string for given emoji name

web_src/js/features/file-view.ts

@@ -3,7 +3,7 @@ import {newRenderPlugin3DViewer} from '../render/plugins/3d-viewer.ts';
 import {newRenderPluginPdfViewer} from '../render/plugins/pdf-viewer.ts';
 import {registerGlobalInitFunc} from '../modules/observer.ts';
 import {createElementFromHTML, showElem, toggleClass} from '../utils/dom.ts';
-import {htmlEscape} from 'escape-goat';
+import {html} from '../utils/html.ts';
 import {basename} from '../utils.ts';
 
 const plugins: FileRenderPlugin[] = [];
@@ -54,7 +54,7 @@ async function renderRawFileToContainer(container: HTMLElement, rawFileLink: str
   container.replaceChildren(elViewRawPrompt);
 
   if (errorMsg) {
-    const elErrorMessage = createElementFromHTML(htmlEscape`<div class="ui error message">${errorMsg}</div>`);
+    const elErrorMessage = createElementFromHTML(html`<div class="ui error message">${errorMsg}</div>`);
     elViewRawPrompt.insertAdjacentElement('afterbegin', elErrorMessage);
   }
 }

web_src/js/features/repo-editor.ts

@@ -1,4 +1,4 @@
-import {htmlEscape} from 'escape-goat';
+import {html, htmlRaw} from '../utils/html.ts';
 import {createCodeEditor} from './codeeditor.ts';
 import {hideElem, queryElems, showElem, createElementFromHTML} from '../utils/dom.ts';
 import {attachRefIssueContextPopup} from './contextpopup.ts';
@@ -87,10 +87,10 @@ export function initRepoEditor() {
         if (i < parts.length - 1) {
           if (trimValue.length) {
             const linkElement = createElementFromHTML(
-              `<span class="section"><a href="#">${htmlEscape(value)}</a></span>`,
+              html`<span class="section"><a href="#">${value}</a></span>`,
             );
             const dividerElement = createElementFromHTML(
-              `<div class="breadcrumb-divider">/</div>`,
+              html`<div class="breadcrumb-divider">/</div>`,
             );
             links.push(linkElement);
             dividers.push(dividerElement);
@@ -113,7 +113,7 @@ export function initRepoEditor() {
       if (!warningDiv) {
         warningDiv = document.createElement('div');
         warningDiv.classList.add('ui', 'warning', 'message', 'flash-message', 'flash-warning', 'space-related');
-        warningDiv.innerHTML = '<p>File path contains leading or trailing whitespace.</p>';
+        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');
@@ -196,7 +196,8 @@ export function initRepoEditor() {
   })();
 }
 
-export function renderPreviewPanelContent(previewPanel: Element, content: string) {
+export function renderPreviewPanelContent(previewPanel: Element, htmlContent: string) {
-  previewPanel.innerHTML = `<div class="render-content markup">${content}</div>`;
+  // the content is from the server, so it is safe to use innerHTML
+  previewPanel.innerHTML = html`<div class="render-content markup">${htmlRaw(htmlContent)}</div>`;
   attachRefIssueContextPopup(previewPanel.querySelectorAll('p .ref-issue'));
 }

web_src/js/features/repo-issue-list.ts

@@ -1,6 +1,6 @@
 import {updateIssuesMeta} from './repo-common.ts';
 import {toggleElem, queryElems, isElemVisible} from '../utils/dom.ts';
-import {htmlEscape} from 'escape-goat';
+import {html} from '../utils/html.ts';
 import {confirmModal} from './comp/ConfirmModal.ts';
 import {showErrorToast} from '../modules/toast.ts';
 import {createSortable} from '../modules/sortable.ts';
@@ -138,10 +138,10 @@ function initDropdownUserRemoteSearch(el: Element) {
         // the content is provided by backend IssuePosters handler
         processedResults.length = 0;
         for (const item of resp.results) {
-          let html = `<img class="ui avatar tw-align-middle" src="${htmlEscape(item.avatar_link)}" aria-hidden="true" alt width="20" height="20"><span class="gt-ellipsis">${htmlEscape(item.username)}</span>`;
+          let nameHtml = html`<img class="ui avatar tw-align-middle" src="${item.avatar_link}" aria-hidden="true" alt width="20" height="20"><span class="gt-ellipsis">${item.username}</span>`;
-          if (item.full_name) html += `<span class="search-fullname tw-ml-2">${htmlEscape(item.full_name)}</span>`;
+          if (item.full_name) nameHtml += html`<span class="search-fullname tw-ml-2">${item.full_name}</span>`;
           if (selectedUsername.toLowerCase() === item.username.toLowerCase()) selectedUsername = item.username;
-          processedResults.push({value: item.username, name: html});
+          processedResults.push({value: item.username, name: nameHtml});
         }
         resp.results = processedResults;
         return resp;

web_src/js/features/repo-issue.ts

@@ -1,4 +1,4 @@
-import {htmlEscape} from 'escape-goat';
+import {html, htmlEscape} from '../utils/html.ts';
 import {createTippy, showTemporaryTooltip} from '../modules/tippy.ts';
 import {
   addDelegatedEventListener,
@@ -46,8 +46,7 @@ export function initRepoIssueSidebarDependency() {
           if (String(issue.id) === currIssueId) continue;
           filteredResponse.results.push({
             value: issue.id,
-            name: `<div class="gt-ellipsis">#${issue.number} ${htmlEscape(issue.title)}</div>
+            name: html`<div class="gt-ellipsis">#${issue.number} ${issue.title}</div><div class="text small tw-break-anywhere">${issue.repository.full_name}</div>`,
-<div class="text small tw-break-anywhere">${htmlEscape(issue.repository.full_name)}</div>`,
           });
         }
         return filteredResponse;

web_src/js/features/repo-new.ts

@@ -1,5 +1,5 @@
 import {hideElem, querySingleVisibleElem, showElem, toggleElem} from '../utils/dom.ts';
-import {htmlEscape} from 'escape-goat';
+import {htmlEscape} from '../utils/html.ts';
 import {fomanticQuery} from '../modules/fomantic/base.ts';
 import {sanitizeRepoName} from './repo-common.ts';
 

web_src/js/features/repo-wiki.ts

@@ -2,6 +2,7 @@ import {validateTextareaNonEmpty, initComboMarkdownEditor} from './comp/ComboMar
 import {fomanticMobileScreen} from '../modules/fomantic.ts';
 import {POST} from '../modules/fetch.ts';
 import type {ComboMarkdownEditor} from './comp/ComboMarkdownEditor.ts';
+import {html, htmlRaw} from '../utils/html.ts';
 
 async function initRepoWikiFormEditor() {
   const editArea = document.querySelector<HTMLTextAreaElement>('.repository.wiki .combo-markdown-editor textarea');
@@ -30,7 +31,7 @@ async function initRepoWikiFormEditor() {
         const response = await POST(editor.previewUrl, {data: formData});
         const data = await response.text();
         lastContent = newContent;
-        previewTarget.innerHTML = `<div class="render-content markup ui segment">${data}</div>`;
+        previewTarget.innerHTML = html`<div class="render-content markup ui segment">${htmlRaw(data)}</div>`;
       } catch (error) {
         console.error('Error rendering preview:', error);
       } finally {

web_src/js/features/tribute.ts

@@ -1,5 +1,5 @@
 import {emojiKeys, emojiHTML, emojiString} from './emoji.ts';
-import {htmlEscape} from 'escape-goat';
+import {html, htmlRaw} from '../utils/html.ts';
 
 type TributeItem = Record<string, any>;
 
@@ -26,17 +26,18 @@ export async function attachTribute(element: HTMLElement) {
         return emojiString(item.original);
       },
       menuItemTemplate: (item: TributeItem) => {
-        return `<div class="tribute-item">${emojiHTML(item.original)}<span>${htmlEscape(item.original)}</span></div>`;
+        return html`<div class="tribute-item">${htmlRaw(emojiHTML(item.original))}<span>${item.original}</span></div>`;
       },
     }, { // mentions
       values: window.config.mentionValues ?? [],
       requireLeadingSpace: true,
       menuItemTemplate: (item: TributeItem) => {
-        return `
+        const fullNameHtml = item.original.fullname && item.original.fullname !== '' ? html`<span class="fullname">${item.original.fullname}</span>` : '';
+        return html`
           <div class="tribute-item">
-            <img alt src="${htmlEscape(item.original.avatar)}" width="21" height="21"/>
+            <img alt src="${item.original.avatar}" width="21" height="21"/>
-            <span class="name">${htmlEscape(item.original.name)}</span>
+            <span class="name">${item.original.name}</span>
-            ${item.original.fullname && item.original.fullname !== '' ? `<span class="fullname">${htmlEscape(item.original.fullname)}</span>` : ''}
+            ${htmlRaw(fullNameHtml)}
           </div>
         `;
       },

web_src/js/markup/html2markdown.ts

@@ -1,4 +1,4 @@
-import {htmlEscape} from 'escape-goat';
+import {html, htmlRaw} from '../utils/html.ts';
 
 type Processor = (el: HTMLElement) => string | HTMLElement | void;
 
@@ -38,10 +38,10 @@ function prepareProcessors(ctx:ProcessorContext): Processors {
     IMG(el: HTMLElement) {
       const alt = el.getAttribute('alt') || 'image';
       const src = el.getAttribute('src');
-      const widthAttr = el.hasAttribute('width') ? ` width="${htmlEscape(el.getAttribute('width') || '')}"` : '';
+      const widthAttr = el.hasAttribute('width') ? htmlRaw` width="${el.getAttribute('width') || ''}"` : '';
-      const heightAttr = el.hasAttribute('height') ? ` height="${htmlEscape(el.getAttribute('height') || '')}"` : '';
+      const heightAttr = el.hasAttribute('height') ? htmlRaw` height="${el.getAttribute('height') || ''}"` : '';
       if (widthAttr || heightAttr) {
-        return `<img alt="${htmlEscape(alt)}"${widthAttr}${heightAttr} src="${htmlEscape(src)}">`;
+        return html`<img alt="${alt}"${widthAttr}${heightAttr} src="${src}">`;
       }
       return `![${alt}](${src})`;
     },

web_src/js/markup/mermaid.ts

@@ -2,6 +2,7 @@ import {isDarkTheme} from '../utils.ts';
 import {makeCodeCopyButton} from './codecopy.ts';
 import {displayError} from './common.ts';
 import {queryElems} from '../utils/dom.ts';
+import {html, htmlRaw} from '../utils/html.ts';
 
 const {mermaidMaxSourceCharacters} = window.config;
 
@@ -46,7 +47,7 @@ export async function initMarkupCodeMermaid(elMarkup: HTMLElement): Promise<void
 
       const iframe = document.createElement('iframe');
       iframe.classList.add('markup-content-iframe', 'tw-invisible');
-      iframe.srcdoc = `<html><head><style>${iframeCss}</style></head><body>${svg}</body></html>`;
+      iframe.srcdoc = html`<html><head><style>${htmlRaw(iframeCss)}</style></head><body>${htmlRaw(svg)}</body></html>`;
 
       const mermaidBlock = document.createElement('div');
       mermaidBlock.classList.add('mermaid-block', 'is-loading', 'tw-hidden');

web_src/js/modules/tippy.ts

@@ -2,6 +2,7 @@ import tippy, {followCursor} from 'tippy.js';
 import {isDocumentFragmentOrElementNode} from '../utils/dom.ts';
 import {formatDatetime} from '../utils/time.ts';
 import type {Content, Instance, Placement, Props} from 'tippy.js';
+import {html} from '../utils/html.ts';
 
 type TippyOpts = {
   role?: string,
@@ -9,7 +10,7 @@ type TippyOpts = {
 } & Partial<Props>;
 
 const visibleInstances = new Set<Instance>();
-const arrowSvg = `<svg width="16" height="7"><path d="m0 7 8-7 8 7Z" class="tippy-svg-arrow-outer"/><path d="m0 8 8-7 8 7Z" class="tippy-svg-arrow-inner"/></svg>`;
+const arrowSvg = html`<svg width="16" height="7"><path d="m0 7 8-7 8 7Z" class="tippy-svg-arrow-outer"/><path d="m0 8 8-7 8 7Z" class="tippy-svg-arrow-inner"/></svg>`;
 
 export function createTippy(target: Element, opts: TippyOpts = {}): Instance {
   // the callback functions should be destructured from opts,

web_src/js/modules/toast.ts

@@ -1,4 +1,4 @@
-import {htmlEscape} from 'escape-goat';
+import {htmlEscape} from '../utils/html.ts';
 import {svg} from '../svg.ts';
 import {animateOnce, queryElems, showElem} from '../utils/dom.ts';
 import Toastify from 'toastify-js'; // don't use "async import", because when network error occurs, the "async import" also fails and nothing is shown

web_src/js/svg.ts

@@ -1,5 +1,6 @@
 import {defineComponent, h, type PropType} from 'vue';
 import {parseDom, serializeXml} from './utils.ts';
+import {html, htmlRaw} from './utils/html.ts';
 import giteaDoubleChevronLeft from '../../public/assets/img/svg/gitea-double-chevron-left.svg';
 import giteaDoubleChevronRight from '../../public/assets/img/svg/gitea-double-chevron-right.svg';
 import giteaEmptyCheckbox from '../../public/assets/img/svg/gitea-empty-checkbox.svg';
@@ -220,7 +221,7 @@ export const SvgIcon = defineComponent({
     const classes = Array.from(svgOuter.classList);
     if (this.symbolId) {
       classes.push('tw-hidden', 'svg-symbol-container');
-      svgInnerHtml = `<symbol id="${this.symbolId}" viewBox="${attrs['^viewBox']}">${svgInnerHtml}</symbol>`;
+      svgInnerHtml = html`<symbol id="${this.symbolId}" viewBox="${attrs['^viewBox']}">${htmlRaw(svgInnerHtml)}</symbol>`;
     }
     // create VNode
     return h('svg', {

web_src/js/utils/dom.ts

@@ -314,6 +314,7 @@ export function replaceTextareaSelection(textarea: HTMLTextAreaElement, text: st
 export function createElementFromHTML<T extends HTMLElement>(htmlString: string): T {
   htmlString = htmlString.trim();
   // some tags like "tr" are special, it must use a correct parent container to create
+  // eslint-disable-next-line github/unescaped-html-literal -- FIXME: maybe we need to use other approaches to create elements from HTML, e.g. using DOMParser
   if (htmlString.startsWith('<tr')) {
     const container = document.createElement('table');
     container.innerHTML = htmlString;

web_src/js/utils/html.test.ts

@@ -0,0 +1,8 @@
+import {html, htmlEscape, htmlRaw} from './html.ts';
+
+test('html', async () => {
+  expect(html`<a>${'<>&\'"'}</a>`).toBe(`<a>&lt;&gt;&amp;&#39;&quot;</a>`);
+  expect(html`<a>${htmlRaw('<img>')}</a>`).toBe(`<a><img></a>`);
+  expect(html`<a>${htmlRaw`<img ${'&'}>`}</a>`).toBe(`<a><img &amp;></a>`);
+  expect(htmlEscape(`<a></a>`)).toBe(`&lt;a&gt;&lt;/a&gt;`);
+});

web_src/js/utils/html.ts

@@ -0,0 +1,32 @@
+export function htmlEscape(s: string, ...args: Array<any>): string {
+  if (args.length !== 0) throw new Error('use html or htmlRaw instead of htmlEscape'); // check legacy usages
+  return s.replace(/&/g, '&amp;')
+    .replace(/"/g, '&quot;')
+    .replace(/'/g, '&#39;')
+    .replace(/</g, '&lt;')
+    .replace(/>/g, '&gt;');
+}
+
+class rawObject {
+  private readonly value: string;
+  constructor(v: string) { this.value = v }
+  toString(): string { return this.value }
+}
+
+export function html(tmpl: TemplateStringsArray, ...parts: Array<any>): string {
+  let output = tmpl[0];
+  for (let i = 0; i < parts.length; i++) {
+    const value = parts[i];
+    const valueEscaped = (value instanceof rawObject) ? value.toString() : htmlEscape(String(parts[i]));
+    output = output + valueEscaped + tmpl[i + 1];
+  }
+  return output;
+}
+
+export function htmlRaw(s: string|TemplateStringsArray, ...tmplParts: Array<any>): rawObject {
+  if (typeof s === 'string') {
+    if (tmplParts.length !== 0) throw new Error("either htmlRaw('str') or htmlRaw`tmpl`");
+    return new rawObject(s);
+  }
+  return new rawObject(html(s, ...tmplParts));
+}