frontend: generic lazy loader for webcomponents (#8510)

After seeing #8111 use a webcomponent, I think that they are a neat usecase for Forgejo where most of the frontend is backend-generated, with some "island of enhancements".

I am considering using a webcomponent for the CITATION management (last occurrence of [`Blob.GetBlobContent`](https://codeberg.org/forgejo/forgejo/issues/8222)), however I noticed that the developer experience wasn't ideal.

With this PR it would be very easy to declare a webcomponent, which will be loaded only if needed (I converted `model-viewer` and `pdf-object` to this technique).

Some cleanup in the neighbor webcomponents.

## Testing

1) Create a new repository or use an existing one.
2) Upload a `.pdf` or `.glb`  file (such as https://codeberg.org/forgejo/forgejo/src/branch/forgejo/tests/testdata/data/viewer/Unicode%E2%9D%A4%E2%99%BBTest.glb)
3) Open the Network inspector and view the file in the repository.
    - After a short loading spinner, the PDF or 3D model should be rendered in a viewer
    - the related JS should have been loaded (e.g. http://localhost:3000/assets/js/model-viewer.494bf0cd.js)
    - visiting another page and check that this JS file isn't loaded

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8510
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Reviewed-by: Beowulf <beowulf@beocode.eu>
Co-authored-by: oliverpool <git@olivier.pfad.fr>
Co-committed-by: oliverpool <git@olivier.pfad.fr>

modules/translation/plural_rules.go

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: MIT
 
 // Some useful links:
+// https://codeberg.org/forgejo/forgejo/src/branch/forgejo/web_src/js/webcomponents/relative-time.js
 // https://www.unicode.org/cldr/charts/46/supplemental/language_plural_rules.html
 // https://translate.codeberg.org/languages/$LANGUAGE_CODE/#information
 // https://github.com/WeblateOrg/language-data/blob/main/languages.csv
@@ -16,7 +17,7 @@ import (
 	"forgejo.org/modules/translation/i18n"
 )
 
-// The constants refer to indices below in `PluralRules` and also in i18n.js, keep them in sync!
+// The constants refer to indices below in `PluralRules` and also in web_src/js/webcomponents/relative-time.js, keep them in sync!
 const (
 	PluralRuleDefault    = 0
 	PluralRuleBengali    = 1

templates/repo/settings/lfs_file.tmpl

@@ -31,10 +31,12 @@
 									<strong>{{ctx.Locale.Tr "repo.audio_not_supported_in_browser"}}</strong>
 								</audio>
 							{{else if .IsPDFFile}}
-								<div class="pdf-content is-loading" data-src="{{$.RawFileLink}}" data-fallback-button-text="{{ctx.Locale.Tr "repo.diff.view_file"}}"></div>
+								<lazy-webc tag="pdf-object" src="{{$.RawFileLink}}">
+									<a href="{{$.RawFileLink}}" class="ui basic button">{{ctx.Locale.Tr "repo.diff.view_file"}}</a>
+								</lazy-webc>
 							{{else if .Is3DModelFile}}
 								{{if .IsGLBFile}}
-									<model-viewer src="{{$.RawFileLink}}" ar shadow-intensity="2" camera-controls touch-action="pan-y"></model-viewer>
+									<lazy-webc tag="model-viewer" src="{{$.RawFileLink}}" ar shadow-intensity="2" camera-controls touch-action="pan-y"></lazy-webc>
 								{{else}}
 									<a href="{{$.RawFileLink}}" rel="nofollow">{{ctx.Locale.Tr "repo.file_view_raw"}}!</a>
 								{{end}}

templates/repo/view_file.tmpl

@@ -127,10 +127,12 @@
 							<strong>{{ctx.Locale.Tr "repo.audio_not_supported_in_browser"}}</strong>
 						</audio>
 					{{else if .IsPDFFile}}
-						<div class="pdf-content is-loading" data-src="{{$.RawFileLink}}" data-fallback-button-text="{{ctx.Locale.Tr "repo.diff.view_file"}}"></div>
+						<lazy-webc tag="pdf-object" src="{{$.RawFileLink}}">
+							<a href="{{$.RawFileLink}}" class="ui basic button">{{ctx.Locale.Tr "repo.diff.view_file"}}</a>
+						</lazy-webc>
 					{{else if .Is3DModelFile}}
 						{{if .IsGLBFile}}
-							<model-viewer src="{{$.RawFileLink}}" ar shadow-intensity="2" camera-controls touch-action="pan-y"></model-viewer>
+							<lazy-webc tag="model-viewer" src="{{$.RawFileLink}}" ar shadow-intensity="2" camera-controls touch-action="pan-y"></lazy-webc>
 						{{else}}
 							<a href="{{$.RawFileLink}}" rel="nofollow">{{ctx.Locale.Tr "repo.file_view_raw"}}</a>
 						{{end}}

web_src/css/modules/animations.css

@@ -3,11 +3,13 @@
   100% { transform: translate(-50%, -50%) rotate(360deg); }
 }
 
+lazy-webc,
 .is-loading {
   pointer-events: none !important;
   position: relative !important;
 }
 
+lazy-webc > *,
 .is-loading > * {
   opacity: 0.3;
 }
@@ -17,6 +19,7 @@
   opacity: 0;
 }
 
+lazy-webc::after,
 .is-loading::after {
   content: "";
   position: absolute;
@@ -52,8 +55,7 @@ form.single-button-form.is-loading .button {
 }
 
 .markup pre.is-loading,
-.editor-loading.is-loading,
+.editor-loading.is-loading {
-.pdf-content.is-loading {
   height: var(--height-loading);
 }
 

web_src/css/repo.css

@@ -415,12 +415,14 @@ td .commit-summary {
   max-width: 600px !important;
 }
 
+lazy-webc[tag="model-viewer"],
 model-viewer {
   width: 100%;
   height: 100vh;
 }
 
-.pdf-content {
+lazy-webc[tag="pdf-object"],
+pdf-object {
   width: 100%;
   height: 100vh;
   border: none !important;
@@ -429,10 +431,6 @@ model-viewer {
   justify-content: center;
 }
 
-.pdf-content .pdf-fallback-button {
-  margin: 50px auto;
-}
-
 .repository.file.list .non-diff-file-content .plain-text {
   padding: 1em 2em;
 }

web_src/js/index.js

@@ -22,8 +22,6 @@ import {initRepoIssueContentHistory} from './features/repo-issue-content.js';
 import {initStopwatch} from './features/stopwatch.js';
 import {initFindFileInRepo} from './features/repo-findfile.js';
 import {initCommentContent, initMarkupContent} from './markup/content.js';
-import {initPdfViewer} from './render/pdf.js';
-import {initGltfViewer} from './render/gltf.js';
 
 import {initUserAuthOauth2, initUserAuth} from './features/user-auth.js';
 import {
@@ -189,8 +187,6 @@ onDomReady(() => {
   initUserAuthWebAuthnRegister();
   initUserAuth();
   initRepoDiffView();
-  initPdfViewer();
-  initGltfViewer();
   initScopedAccessTokenCategories();
   initColorPickers();
 

web_src/js/render/gltf.js

@@ -1,6 +0,0 @@
-export async function initGltfViewer() {
-  const els = document.querySelectorAll('model-viewer');
-  if (!els.length) return;
-
-  await import(/* webpackChunkName: "@google/model-viewer" */'@google/model-viewer');
-}

web_src/js/render/pdf.js

@@ -1,19 +0,0 @@
-import {htmlEscape} from 'escape-goat';
-
-export async function initPdfViewer() {
-  const els = document.querySelectorAll('.pdf-content');
-  if (!els.length) return;
-
-  const pdfobject = await import(/* webpackChunkName: "pdfobject" */'pdfobject');
-
-  for (const el of els) {
-    const src = el.getAttribute('data-src');
-    const fallbackText = el.getAttribute('data-fallback-button-text');
-    pdfobject.embed(src, el, {
-      fallbackLink: htmlEscape`
-        <a role="button" class="ui basic button pdf-fallback-button" href="[url]">${fallbackText}</a>
-      `,
-    });
-    el.classList.remove('is-loading');
-  }
-}

web_src/js/webcomponents/i18n.js

@@ -1,75 +0,0 @@
-const {pageData} = window.config;
-
-/**
- * A list of plural rules for all languages.
- * `plural_rules.go` defines the index for each of the 14 known plural rules.
- *
- * `pageData.PLURAL_RULE_LANG` is the index of the plural rule for the current language.
- * `pageData.PLURAL_RULE_FALLBACK` is the index of the plural rule for the default language,
- * to be used when a string is not translated in the current language.
- *
- * Each plural rule is a function that maps an amount `n` to the appropriate plural form index.
- * Which index means which rule is specific for each language and also defined in `plural_rules.go`.
- * The actual strings are in `pageData.PLURALSTRINGS_LANG` and `pageData.PLURALSTRINGS_FALLBACK`
- * respectively, which is an array indexed by the plural form index.
- *
- * Links to the language plural rule and form definitions:
- * https://codeberg.org/forgejo/forgejo/src/branch/forgejo/modules/translation/plural_rules.go
- * https://www.unicode.org/cldr/charts/46/supplemental/language_plural_rules.html
- * https://translate.codeberg.org/languages/$LANGUAGE_CODE/#information
- * https://github.com/WeblateOrg/language-data/blob/main/languages.csv
- */
-const PLURAL_RULES = [
-  // [ 0] Common 2-form, e.g. English, German
-  function (n) { return n !== 1 ? 1 : 0 },
-
-  // [ 1] Bengali 2-form
-  function (n) { return n > 1 ? 1 : 0 },
-
-  // [ 2] Icelandic 2-form
-  function (n) { return n % 10 !== 1 || n % 100 === 11 ? 1 : 0 },
-
-  // [ 3] Filipino 2-form
-  function (n) { return n !== 1 && n !== 2 && n !== 3 && (n % 10 === 4 || n % 10 === 6 || n % 10 === 9) ? 1 : 0 },
-
-  // [ 4] One form
-  function (_) { return 0 },
-
-  // [ 5] Czech 3-form
-  function (n) { return (n === 1) ? 0 : (n >= 2 && n <= 4) ? 1 : 2 },
-
-  // [ 6] Russian 3-form
-  function (n) { return n % 10 === 1 && n % 100 !== 11 ? 0 : n % 10 >= 2 && n % 10 <= 4 && (n % 100 < 10 || n % 100 >= 20) ? 1 : 2 },
-
-  // [ 7] Polish 3-form
-  function (n) { return n === 1 ? 0 : n % 10 >= 2 && n % 10 <= 4 && (n % 100 < 10 || n % 100 >= 20) ? 1 : 2 },
-
-  // [ 8] Latvian 3-form
-  function (n) { return (n % 10 === 0 || n % 100 >= 11 && n % 100 <= 19) ? 0 : ((n % 10 === 1 && n % 100 !== 11) ? 1 : 2) },
-
-  // [ 9] Lithunian 3-form
-  function (n) { return (n % 10 === 1 && (n % 100 < 11 || n % 100 > 19)) ? 0 : ((n % 10 >= 2 && n % 10 <= 9 && (n % 100 < 11 || n % 100 > 19)) ? 1 : 2) },
-
-  // [10] French 3-form
-  function (n) { return (n === 0 || n === 1) ? 0 : ((n !== 0 && n % 1000000 === 0) ? 1 : 2) },
-
-  // [11] Catalan 3-form
-  function (n) { return (n === 1) ? 0 : ((n !== 0 && n % 1000000 === 0) ? 1 : 2) },
-
-  // [12] Slovenian 4-form
-  function (n) { return n % 100 === 1 ? 0 : n % 100 === 2 ? 1 : n % 100 === 3 || n % 100 === 4 ? 2 : 3 },
-
-  // [13] Arabic 6-form
-  function (n) { return n === 0 ? 0 : n === 1 ? 1 : n === 2 ? 2 : n % 100 >= 3 && n % 100 <= 10 ? 3 : n % 100 >= 11 ? 4 : 5 },
-];
-
-/**
- * Look up the correct localized plural form for amount `n` for the string with the translation key `key`.
- * If the current language does not contain a translation for this key, returns the text in the default language,
- * or `null` if `suppress_fallback` is set to `true`.
- */
-export function GetPluralizedString(key, n, suppress_fallback) {
-  const result = pageData.PLURALSTRINGS_LANG[key]?.[PLURAL_RULES[pageData.PLURAL_RULE_LANG](n)];
-  if (result || suppress_fallback) return result;
-  return pageData.PLURALSTRINGS_FALLBACK[key][PLURAL_RULES[pageData.PLURAL_RULE_FALLBACK](n)];
-}

web_src/js/webcomponents/index.js

@@ -1,6 +1,5 @@
-import './polyfills.js';
-import './i18n.js';
 import './relative-time.js';
 import './origin-url.js';
 import './overflow-menu.js';
 import './absolute-date.js';
+import './lazy-webc.js'; // infrequently used components should be lazy-loaded with <lazy-webc tag="..." custom-attrs>...</>

web_src/js/webcomponents/lazy-webc.js

@@ -0,0 +1,66 @@
+import {onDomReady} from '../utils/dom.js';
+
+/**
+ * Lazy-load the promise (making it a singleton).
+ * @param {()=>Promise} newPromise Promise factory.
+ * @returns {()=>Promise} Singleton promise
+ */
+function lazyPromise(newPromise) {
+  /** @type {Promise?} */
+  let p;
+  return () => {
+    p ??= newPromise();
+    return p;
+  };
+}
+
+// the following web components will only be loaded if present in the page (to reduce the bundle size for infrequently used components)
+const loadableComponents = {
+  'model-viewer': lazyPromise(() => {
+    return import(/* webpackChunkName: "model-viewer" */ '@google/model-viewer');
+  }),
+  'pdf-object': lazyPromise(() => {
+    return import(/* webpackChunkName: "pdf-object" */ './pdf-object.js');
+  }),
+};
+
+/**
+ * Replace elt with an element having the given tag.
+ * @param {HTMLElement} elt The element to replace.
+ * @param {string} name The tagName of the new element.
+ */
+function replaceTag(elt, name) {
+  const successor = document.createElement(name);
+  // Move the children to the successor
+  while (elt.firstChild) {
+    successor.append(elt.firstChild);
+  }
+  // Copy the attributes to the successor
+  for (let index = elt.attributes.length - 1; index >= 0; --index) {
+    successor.attributes.setNamedItem(elt.attributes[index].cloneNode());
+  }
+  // Replace elt with the successor
+  elt.parentNode.replaceChild(successor, elt);
+}
+
+onDomReady(() => {
+  // The lazy-webc component will replace itself with an element of the type given in the attribute tag.
+  // This seems to be the best way without having to create a global mutationObserver.
+  // See https://codeberg.org/forgejo/forgejo/pulls/8510 for discussion.
+  window.customElements.define(
+    'lazy-webc',
+    class extends HTMLElement {
+      connectedCallback() {
+        const name = this.getAttribute('tag');
+        if (loadableComponents[name]) {
+          loadableComponents[name]().finally(() => {
+            replaceTag(this, name);
+          });
+        } else {
+          console.error('lazy-webc: unknown webcomponent:', name);
+          replaceTag(this, name); // still replace it, maybe it was eagerly defined
+        }
+      }
+    },
+  );
+});

web_src/js/webcomponents/pdf-object.js

@@ -0,0 +1,14 @@
+import pdfobject from 'pdfobject';
+
+window.customElements.define(
+  'pdf-object',
+  class extends HTMLElement {
+    connectedCallback() {
+      // since the web-component is defined after the DOM is ready, it is safe to look at the children.
+      const fallbackLink = this.innerHTML; // eslint-disable-line wc/no-child-traversal-in-connectedcallback
+      pdfobject.embed(this.getAttribute('src'), this, {
+        fallbackLink,
+      });
+    }
+  },
+);

web_src/js/webcomponents/polyfills.js

@@ -1,17 +0,0 @@
-try {
-  // some browsers like PaleMoon don't have full support for Intl.NumberFormat, so do the minimum polyfill to support "relative-time-element"
-  // https://repo.palemoon.org/MoonchildProductions/UXP/issues/2289
-  new Intl.NumberFormat('en', {style: 'unit', unit: 'minute'}).format(1);
-} catch {
-  const intlNumberFormat = Intl.NumberFormat;
-  Intl.NumberFormat = function(locales, options) {
-    if (options.style === 'unit') {
-      return {
-        format(value) {
-          return ` ${value} ${options.unit}`;
-        },
-      };
-    }
-    return intlNumberFormat(locales, options);
-  };
-}

web_src/js/webcomponents/relative-time.js

@@ -1,4 +1,3 @@
-import {GetPluralizedString} from './i18n.js';
 import dayjs from 'dayjs';
 const {pageData} = window.config;
 
@@ -17,8 +16,75 @@ const ABSOLUTE_DATETIME_FORMAT = new Intl.DateTimeFormat(navigator.language, {
 });
 const FALLBACK_DATETIME_FORMAT = new Intl.RelativeTimeFormat(navigator.language, {style: 'long'});
 
+/**
+ * A list of plural rules for all languages.
+ * `plural_rules.go` defines the index for each of the 14 known plural rules.
+ *
+ * `pageData.PLURAL_RULE_LANG` is the index of the plural rule for the current language.
+ * `pageData.PLURAL_RULE_FALLBACK` is the index of the plural rule for the default language,
+ * to be used when a string is not translated in the current language.
+ *
+ * Each plural rule is a function that maps an amount `n` to the appropriate plural form index.
+ * Which index means which rule is specific for each language and also defined in `plural_rules.go`.
+ * The actual strings are in `pageData.PLURALSTRINGS_LANG` and `pageData.PLURALSTRINGS_FALLBACK`
+ * respectively, which is an array indexed by the plural form index.
+ *
+ * Links to the language plural rule and form definitions:
+ * https://codeberg.org/forgejo/forgejo/src/branch/forgejo/modules/translation/plural_rules.go
+ * https://www.unicode.org/cldr/charts/46/supplemental/language_plural_rules.html
+ * https://translate.codeberg.org/languages/$LANGUAGE_CODE/#information
+ * https://github.com/WeblateOrg/language-data/blob/main/languages.csv
+ */
+const PLURAL_RULES = [
+  // [ 0] Common 2-form, e.g. English, German
+  function (n) { return n !== 1 ? 1 : 0 },
+
+  // [ 1] Bengali 2-form
+  function (n) { return n > 1 ? 1 : 0 },
+
+  // [ 2] Icelandic 2-form
+  function (n) { return n % 10 !== 1 || n % 100 === 11 ? 1 : 0 },
+
+  // [ 3] Filipino 2-form
+  function (n) { return n !== 1 && n !== 2 && n !== 3 && (n % 10 === 4 || n % 10 === 6 || n % 10 === 9) ? 1 : 0 },
+
+  // [ 4] One form
+  function (_) { return 0 },
+
+  // [ 5] Czech 3-form
+  function (n) { return (n === 1) ? 0 : (n >= 2 && n <= 4) ? 1 : 2 },
+
+  // [ 6] Russian 3-form
+  function (n) { return n % 10 === 1 && n % 100 !== 11 ? 0 : n % 10 >= 2 && n % 10 <= 4 && (n % 100 < 10 || n % 100 >= 20) ? 1 : 2 },
+
+  // [ 7] Polish 3-form
+  function (n) { return n === 1 ? 0 : n % 10 >= 2 && n % 10 <= 4 && (n % 100 < 10 || n % 100 >= 20) ? 1 : 2 },
+
+  // [ 8] Latvian 3-form
+  function (n) { return (n % 10 === 0 || n % 100 >= 11 && n % 100 <= 19) ? 0 : ((n % 10 === 1 && n % 100 !== 11) ? 1 : 2) },
+
+  // [ 9] Lithunian 3-form
+  function (n) { return (n % 10 === 1 && (n % 100 < 11 || n % 100 > 19)) ? 0 : ((n % 10 >= 2 && n % 10 <= 9 && (n % 100 < 11 || n % 100 > 19)) ? 1 : 2) },
+
+  // [10] French 3-form
+  function (n) { return (n === 0 || n === 1) ? 0 : ((n !== 0 && n % 1000000 === 0) ? 1 : 2) },
+
+  // [11] Catalan 3-form
+  function (n) { return (n === 1) ? 0 : ((n !== 0 && n % 1000000 === 0) ? 1 : 2) },
+
+  // [12] Slovenian 4-form
+  function (n) { return n % 100 === 1 ? 0 : n % 100 === 2 ? 1 : n % 100 === 3 || n % 100 === 4 ? 2 : 3 },
+
+  // [13] Arabic 6-form
+  function (n) { return n === 0 ? 0 : n === 1 ? 1 : n === 2 ? 2 : n % 100 >= 3 && n % 100 <= 10 ? 3 : n % 100 >= 11 ? 4 : 5 },
+];
+
+/**
+ * Look up the correct localized plural form for amount `n` for the string with the translation key `key`.
+ * If the current language does not contain a translation for this key, fallback to the browser's formatting.
+ */
 function GetPluralizedStringOrFallback(key, n, unit) {
-  const translation = GetPluralizedString(key, n, true);
+  const translation = pageData.PLURALSTRINGS_LANG[key]?.[PLURAL_RULES[pageData.PLURAL_RULE_LANG](n)];
   if (translation) return translation.replace('%d', n);
   return FALLBACK_DATETIME_FORMAT.format(-n, unit);
 }