Refactor global init code and add more comments (#33755)

Follow up #33748

Now there are 3 "global" functions:

* registerGlobalSelectorFunc: for all elements matching the selector, eg: `.ui.dropdown`
* registerGlobalInitFunc: for `data-global-init="initInputAutoFocusEnd"`
* registerGlobalEventFunc: for `data-global-click="onCommentReactionButtonClick"`


And introduce `initGlobalInput` to replace old `initAutoFocusEnd` and
`attachDirAuto`, use `data-global-init` to replace fragile
`.js-autofocus-end` selector.

Another benefit is that by the new approach, no matter how many times
`registerGlobalInitFunc` is called, we only need to do one
"querySelectorAll" in the last step, it could slightly improve the
performance.

7 files changed, 135 insertions, 109 deletions

diff --git a/web_src/js/features/autofocus-end.ts b/web_src/js/features/autofocus-end.ts
deleted file mode 100644
index 53e475b543..0000000000
--- a/web_src/js/features/autofocus-end.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-export function initAutoFocusEnd() {
-  for (const el of document.querySelectorAll<HTMLInputElement>('.js-autofocus-end')) {
-    el.focus(); // expects only one such element on one page. If there are many, then the last one gets the focus.
-    el.setSelectionRange(el.value.length, el.value.length);
-  }
-}
diff --git a/web_src/js/features/common-page.ts b/web_src/js/features/common-page.ts
index c5274201f2..235555a73d 100644
--- a/web_src/js/features/common-page.ts
+++ b/web_src/js/features/common-page.ts
@@ -2,7 +2,7 @@ import {GET} from '../modules/fetch.ts';
 import {showGlobalErrorMessage} from '../bootstrap.ts';
 import {fomanticQuery} from '../modules/fomantic/base.ts';
 import {queryElems} from '../utils/dom.ts';
-import {observeAddedElement} from '../modules/observer.ts';
+import {registerGlobalInitFunc, registerGlobalSelectorFunc} from '../modules/observer.ts';
 
 const {appUrl} = window.config;
 
@@ -30,7 +30,7 @@ export function initFootLanguageMenu() {
 
 export function initGlobalDropdown() {
   // do not init "custom" dropdowns, "custom" dropdowns are managed by their own code.
-  observeAddedElement('.ui.dropdown:not(.custom)', (el) => {
+  registerGlobalSelectorFunc('.ui.dropdown:not(.custom)', (el) => {
     const $dropdown = fomanticQuery(el);
     if ($dropdown.data('module-dropdown')) return; // do not re-init if other code has already initialized it.
 
@@ -80,6 +80,25 @@ export function initGlobalTabularMenu() {
   fomanticQuery('.ui.menu.tabular:not(.custom) .item').tab({autoTabActivation: false});
 }
 
+// for performance considerations, it only uses performant syntax
+function attachInputDirAuto(el: Partial<HTMLInputElement | HTMLTextAreaElement>) {
+  if (el.type !== 'hidden' &&
+    el.type !== 'checkbox' &&
+    el.type !== 'radio' &&
+    el.type !== 'range' &&
+    el.type !== 'color') {
+    el.dir = 'auto';
+  }
+}
+
+export function initGlobalInput() {
+  registerGlobalSelectorFunc('input, textarea', attachInputDirAuto);
+  registerGlobalInitFunc('initInputAutoFocusEnd', (el: HTMLInputElement) => {
+    el.focus(); // expects only one such element on one page. If there are many, then the last one gets the focus.
+    el.setSelectionRange(el.value.length, el.value.length);
+  });
+}
+
 /**
  * Too many users set their ROOT_URL to wrong value, and it causes a lot of problems:
  *   * Cross-origin API request without correct cookie
diff --git a/web_src/js/features/repo-diff.ts b/web_src/js/features/repo-diff.ts
index f1e441a133..1ecd00f1af 100644
--- a/web_src/js/features/repo-diff.ts
+++ b/web_src/js/features/repo-diff.ts
@@ -10,7 +10,7 @@ import {POST, GET} from '../modules/fetch.ts';
 import {createTippy} from '../modules/tippy.ts';
 import {invertFileFolding} from './file-fold.ts';
 import {parseDom} from '../utils.ts';
-import {observeAddedElement} from '../modules/observer.ts';
+import {registerGlobalSelectorFunc} from '../modules/observer.ts';
 
 const {i18n} = window.config;
 
@@ -254,7 +254,7 @@ export function initRepoDiffView() {
   initExpandAndCollapseFilesButton();
   initRepoDiffHashChangeListener();
 
-  observeAddedElement('#diff-file-boxes .diff-file-box', initRepoDiffFileBox);
+  registerGlobalSelectorFunc('#diff-file-boxes .diff-file-box', initRepoDiffFileBox);
   addDelegatedEventListener(document, 'click', '.fold-file', (el) => {
     invertFileFolding(el.closest('.file-content'), el);
   });
diff --git a/web_src/js/index.ts b/web_src/js/index.ts
index 2e253870c0..f48074316e 100644
--- a/web_src/js/index.ts
+++ b/web_src/js/index.ts
@@ -11,7 +11,6 @@ import {initImageDiff} from './features/imagediff.ts';
 import {initRepoMigration} from './features/repo-migration.ts';
 import {initRepoProject} from './features/repo-projects.ts';
 import {initTableSort} from './features/tablesort.ts';
-import {initAutoFocusEnd} from './features/autofocus-end.ts';
 import {initAdminUserListSearchForm} from './features/admin/users.ts';
 import {initAdminConfigs} from './features/admin/config.ts';
 import {initMarkupAnchors} from './markup/anchors.ts';
@@ -62,62 +61,23 @@ import {initRepoContributors} from './features/contributors.ts';
 import {initRepoCodeFrequency} from './features/code-frequency.ts';
 import {initRepoRecentCommits} from './features/recent-commits.ts';
 import {initRepoDiffCommitBranchesAndTags} from './features/repo-diff-commit.ts';
-import {initAddedElementObserver} from './modules/observer.ts';
+import {initGlobalSelectorObserver} from './modules/observer.ts';
 import {initRepositorySearch} from './features/repo-search.ts';
 import {initColorPickers} from './features/colorpicker.ts';
 import {initAdminSelfCheck} from './features/admin/selfcheck.ts';
 import {initOAuth2SettingsDisableCheckbox} from './features/oauth2-settings.ts';
 import {initGlobalFetchAction} from './features/common-fetch-action.ts';
-import {
-  initFootLanguageMenu,
-  initGlobalDropdown,
-  initGlobalTabularMenu,
-  initHeadNavbarContentToggle,
-} from './features/common-page.ts';
-import {
-  initGlobalButtonClickOnEnter,
-  initGlobalButtons,
-  initGlobalDeleteButton,
-} from './features/common-button.ts';
-import {
-  initGlobalComboMarkdownEditor,
-  initGlobalEnterQuickSubmit,
-  initGlobalFormDirtyLeaveConfirm,
-} from './features/common-form.ts';
+import {initFootLanguageMenu, initGlobalDropdown, initGlobalInput, initGlobalTabularMenu, initHeadNavbarContentToggle} from './features/common-page.ts';
+import {initGlobalButtonClickOnEnter, initGlobalButtons, initGlobalDeleteButton} from './features/common-button.ts';
+import {initGlobalComboMarkdownEditor, initGlobalEnterQuickSubmit, initGlobalFormDirtyLeaveConfirm} from './features/common-form.ts';
+import {callInitFunctions} from './modules/init.ts';
 
 initGiteaFomantic();
-initAddedElementObserver();
 initSubmitEventPolyfill();
 
-function callInitFunctions(functions: (() => any)[]) {
-  // Start performance trace by accessing a URL by "https://localhost/?_ui_performance_trace=1" or "https://localhost/?key=value&_ui_performance_trace=1"
-  // It is a quick check, no side effect so no need to do slow URL parsing.
-  const initStart = performance.now();
-  if (window.location.search.includes('_ui_performance_trace=1')) {
-    let results: {name: string, dur: number}[] = [];
-    for (const func of functions) {
-      const start = performance.now();
-      func();
-      results.push({name: func.name, dur: performance.now() - start});
-    }
-    results = results.sort((a, b) => b.dur - a.dur);
-    for (let i = 0; i < 20 && i < results.length; i++) {
-      // eslint-disable-next-line no-console
-      console.log(`performance trace: ${results[i].name} ${results[i].dur.toFixed(3)}`);
-    }
-  } else {
-    for (const func of functions) {
-      func();
-    }
-  }
-  const initDur = performance.now() - initStart;
-  if (initDur > 500) {
-    console.error(`slow init functions took ${initDur.toFixed(3)}ms`);
-  }
-}
-
 onDomReady(() => {
-  callInitFunctions([
+  const initStartTime = performance.now();
+  const initPerformanceTracer = callInitFunctions([
     initGlobalDropdown,
     initGlobalTabularMenu,
     initGlobalFetchAction,
@@ -129,6 +89,7 @@ onDomReady(() => {
     initGlobalFormDirtyLeaveConfirm,
     initGlobalComboMarkdownEditor,
     initGlobalDeleteButton,
+    initGlobalInput,
 
     initCommonOrganization,
     initCommonIssueListQuickGoto,
@@ -150,7 +111,6 @@ onDomReady(() => {
     initSshKeyFormParser,
     initStopwatch,
     initTableSort,
-    initAutoFocusEnd,
     initFindFileInRepo,
     initCopyContent,
 
@@ -212,4 +172,13 @@ onDomReady(() => {
 
     initOAuth2SettingsDisableCheckbox,
   ]);
+
+  // it must be the last one, then the "querySelectorAll" only needs to be executed once for global init functions.
+  initGlobalSelectorObserver(initPerformanceTracer);
+  if (initPerformanceTracer) initPerformanceTracer.printResults();
+
+  const initDur = performance.now() - initStartTime;
+  if (initDur > 500) {
+    console.error(`slow init functions took ${initDur.toFixed(3)}ms`);
+  }
 });
diff --git a/web_src/js/modules/init.ts b/web_src/js/modules/init.ts
new file mode 100644
index 0000000000..538fafd83f
--- /dev/null
+++ b/web_src/js/modules/init.ts
@@ -0,0 +1,26 @@
+export class InitPerformanceTracer {
+  results: {name: string, dur: number}[] = [];
+  recordCall(name: string, func: ()=>void) {
+    const start = performance.now();
+    func();
+    this.results.push({name, dur: performance.now() - start});
+  }
+  printResults() {
+    this.results = this.results.sort((a, b) => b.dur - a.dur);
+    for (let i = 0; i < 20 && i < this.results.length; i++) {
+      console.info(`performance trace: ${this.results[i].name} ${this.results[i].dur.toFixed(3)}`);
+    }
+  }
+}
+
+export function callInitFunctions(functions: (() => any)[]): InitPerformanceTracer | null {
+  // Start performance trace by accessing a URL by "https://localhost/?_ui_performance_trace=1" or "https://localhost/?key=value&_ui_performance_trace=1"
+  // It is a quick check, no side effect so no need to do slow URL parsing.
+  const perfTracer = !window.location.search.includes('_ui_performance_trace=1') ? null : new InitPerformanceTracer();
+  if (perfTracer) {
+    for (const func of functions) perfTracer.recordCall(func.name, func);
+  } else {
+    for (const func of functions) func();
+  }
+  return perfTracer;
+}
diff --git a/web_src/js/modules/observer.ts b/web_src/js/modules/observer.ts
index 57d0db31c7..f60c033cf2 100644
--- a/web_src/js/modules/observer.ts
+++ b/web_src/js/modules/observer.ts
@@ -1,52 +1,73 @@
 import {isDocumentFragmentOrElementNode} from '../utils/dom.ts';
+import type {Promisable} from 'type-fest';
+import type {InitPerformanceTracer} from './init.ts';
 
-type DirElement = HTMLInputElement | HTMLTextAreaElement;
+let globalSelectorObserverInited = false;
 
-// for performance considerations, it only uses performant syntax
-function attachDirAuto(el: Partial<DirElement>) {
-  if (el.type !== 'hidden' &&
-      el.type !== 'checkbox' &&
-      el.type !== 'radio' &&
-      el.type !== 'range' &&
-      el.type !== 'color') {
-    el.dir = 'auto';
+type SelectorHandler = {selector: string, handler: (el: HTMLElement) => void};
+const selectorHandlers: SelectorHandler[] = [];
+
+type GlobalEventFunc<T extends HTMLElement, E extends Event> = (el: T, e: E) => Promisable<void>;
+const globalEventFuncs: Record<string, GlobalEventFunc<HTMLElement, Event>> = {};
+
+type GlobalInitFunc<T extends HTMLElement> = (el: T) => Promisable<void>;
+const globalInitFuncs: Record<string, GlobalInitFunc<HTMLElement>> = {};
+
+// It handles the global events for all `<div data-global-click="onSomeElemClick"></div>` elements.
+export function registerGlobalEventFunc<T extends HTMLElement, E extends Event>(event: string, name: string, func: GlobalEventFunc<T, E>) {
+  globalEventFuncs[`${event}:${name}`] = func as GlobalEventFunc<HTMLElement, Event>;
+}
+
+// It handles the global init functions by a selector, for example:
+// > registerGlobalSelectorObserver('.ui.dropdown:not(.custom)', (el) => { initDropdown(el, ...) });
+export function registerGlobalSelectorFunc(selector: string, handler: (el: HTMLElement) => void) {
+  selectorHandlers.push({selector, handler});
+  // Then initAddedElementObserver will call this handler for all existing elements after all handlers are added.
+  // This approach makes the init stage only need to do one "querySelectorAll".
+  if (!globalSelectorObserverInited) return;
+  for (const el of document.querySelectorAll<HTMLElement>(selector)) {
+    handler(el);
   }
 }
 
-type GlobalInitFunc<T extends HTMLElement> = (el: T) => void | Promise<void>;
-const globalInitFuncs: Record<string, GlobalInitFunc<HTMLElement>> = {};
-function attachGlobalInit(el: HTMLElement) {
+// It handles the global init functions for all `<div data-global-int="initSomeElem"></div>` elements.
+export function registerGlobalInitFunc<T extends HTMLElement>(name: string, handler: GlobalInitFunc<T>) {
+  globalInitFuncs[name] = handler as GlobalInitFunc<HTMLElement>;
+  // The "global init" functions are managed internally and called by callGlobalInitFunc
+  // They must be ready before initGlobalSelectorObserver is called.
+  if (globalSelectorObserverInited) throw new Error('registerGlobalInitFunc() must be called before initGlobalSelectorObserver()');
+}
+
+function callGlobalInitFunc(el: HTMLElement) {
   const initFunc = el.getAttribute('data-global-init');
   const func = globalInitFuncs[initFunc];
   if (!func) throw new Error(`Global init function "${initFunc}" not found`);
+
+  type GiteaGlobalInitElement = Partial<HTMLElement> & {_giteaGlobalInited: boolean};
+  if ((el as GiteaGlobalInitElement)._giteaGlobalInited) throw new Error(`Global init function "${initFunc}" already executed`);
+  (el as GiteaGlobalInitElement)._giteaGlobalInited = true;
   func(el);
 }
 
-type GlobalEventFunc<T extends HTMLElement, E extends Event> = (el: T, e: E) => (void | Promise<void>);
-const globalEventFuncs: Record<string, GlobalEventFunc<HTMLElement, Event>> = {};
-export function registerGlobalEventFunc<T extends HTMLElement, E extends Event>(event: string, name: string, func: GlobalEventFunc<T, E>) {
-  globalEventFuncs[`${event}:${name}`] = func as any;
+function attachGlobalEvents() {
+  // add global "[data-global-click]" event handler
+  document.addEventListener('click', (e) => {
+    const elem = (e.target as HTMLElement).closest<HTMLElement>('[data-global-click]');
+    if (!elem) return;
+    const funcName = elem.getAttribute('data-global-click');
+    const func = globalEventFuncs[`click:${funcName}`];
+    if (!func) throw new Error(`Global event function "click:${funcName}" not found`);
+    func(elem, e);
+  });
 }
 
-type SelectorHandler = {
-  selector: string,
-  handler: (el: HTMLElement) => void,
-};
+export function initGlobalSelectorObserver(perfTracer?: InitPerformanceTracer): void {
+  if (globalSelectorObserverInited) throw new Error('initGlobalSelectorObserver() already called');
+  globalSelectorObserverInited = true;
 
-const selectorHandlers: SelectorHandler[] = [
-  {selector: 'input, textarea', handler: attachDirAuto},
-  {selector: '[data-global-init]', handler: attachGlobalInit},
-];
+  attachGlobalEvents();
 
-export function observeAddedElement(selector: string, handler: (el: HTMLElement) => void) {
-  selectorHandlers.push({selector, handler});
-  const docNodes = document.querySelectorAll<HTMLElement>(selector);
-  for (const el of docNodes) {
-    handler(el);
-  }
-}
-
-export function initAddedElementObserver(): void {
+  selectorHandlers.push({selector: '[data-global-init]', handler: callGlobalInitFunc});
   const observer = new MutationObserver((mutationList) => {
     const len = mutationList.length;
     for (let i = 0; i < len; i++) {
@@ -60,30 +81,27 @@ export function initAddedElementObserver(): void {
           if (addedNode.matches(selector)) {
             handler(addedNode);
           }
-          const children = addedNode.querySelectorAll<HTMLElement>(selector);
-          for (const el of children) {
+          for (const el of addedNode.querySelectorAll<HTMLElement>(selector)) {
             handler(el);
           }
         }
       }
     }
   });
-
-  for (const {selector, handler} of selectorHandlers) {
-    const docNodes = document.querySelectorAll<HTMLElement>(selector);
-    for (const el of docNodes) {
-      handler(el);
+  if (perfTracer) {
+    for (const {selector, handler} of selectorHandlers) {
+      perfTracer.recordCall(`initGlobalSelectorObserver ${selector}`, () => {
+        for (const el of document.querySelectorAll<HTMLElement>(selector)) {
+          handler(el);
+        }
+      });
+    }
+  } else {
+    for (const {selector, handler} of selectorHandlers) {
+      for (const el of document.querySelectorAll<HTMLElement>(selector)) {
+        handler(el);
+      }
     }
   }
-
   observer.observe(document, {subtree: true, childList: true});
-
-  document.addEventListener('click', (e) => {
-    const elem = (e.target as HTMLElement).closest<HTMLElement>('[data-global-click]');
-    if (!elem) return;
-    const funcName = elem.getAttribute('data-global-click');
-    const func = globalEventFuncs[`click:${funcName}`];
-    if (!func) throw new Error(`Global event function "click:${funcName}" not found`);
-    func(elem, e);
-  });
 }
diff --git a/web_src/js/utils/dom.ts b/web_src/js/utils/dom.ts
index 603f967b34..4d15784e6e 100644
--- a/web_src/js/utils/dom.ts
+++ b/web_src/js/utils/dom.ts
@@ -355,7 +355,7 @@ export function querySingleVisibleElem<T extends HTMLElement>(parent: Element, s
   return candidates.length ? candidates[0] as T : null;
 }
 
-export function addDelegatedEventListener<T extends HTMLElement, E extends Event>(parent: Node, type: string, selector: string, listener: (elem: T, e: E) => void | Promise<any>, options?: boolean | AddEventListenerOptions) {
+export function addDelegatedEventListener<T extends HTMLElement, E extends Event>(parent: Node, type: string, selector: string, listener: (elem: T, e: E) => Promisable<void>, options?: boolean | AddEventListenerOptions) {
   parent.addEventListener(type, (e: Event) => {
     const elem = (e.target as HTMLElement).closest(selector);
     if (!elem) return;