fix(module:code-editor): load Monaco only once

components/code-editor/code-editor.service.ts

@@ -5,7 +5,7 @@
 
 import { DOCUMENT } from '@angular/common';
 import { Inject, Injectable, OnDestroy } from '@angular/core';
-import { BehaviorSubject, Observable, of as observableOf, Subject, Subscription } from 'rxjs';
+import { BehaviorSubject, Observable, of, ReplaySubject, Subscription } from 'rxjs';
 import { map, tap } from 'rxjs/operators';
 
 import { CodeEditorConfig, NzConfigService } from 'ng-zorro-antd/core/config';
@@ -26,14 +26,22 @@ function tryTriggerFunc(fn?: (...args: NzSafeAny[]) => NzSafeAny): (...args: NzS
   };
 }
 
+// Caretaker note: previously, these were `NzCodeEditorService` properties.
+// They're kept as static variables because this will allow loading Monaco only once.
+// This applies to micro frontend apps with multiple Angular apps or a single Angular app
+// that can be bootstrapped and destroyed multiple times (e.g. using Webpack module federation).
+// Root providers are re-initialized each time the app is bootstrapped. Platform providers aren't.
+// We can't make the `NzCodeEditorService` to be a platform provider (`@Injectable({ providedIn: 'platform' })`)
+// since it depends on other root providers.
+const loaded$ = new ReplaySubject<boolean>(1);
+let loadingStatus = NzCodeEditorLoadingStatus.UNLOAD;
+
 @Injectable({
   providedIn: 'root'
 })
 export class NzCodeEditorService implements OnDestroy {
   private document: Document;
   private firstEditorInitialized = false;
-  private loaded$ = new Subject<boolean>();
-  private loadingStatus = NzCodeEditorLoadingStatus.UNLOAD;
   private option: JoinedEditorOptions = {};
   private config: CodeEditorConfig;
   private subscription: Subscription | null;
@@ -70,12 +78,12 @@ export class NzCodeEditorService implements OnDestroy {
   }
 
   requestToInit(): Observable<JoinedEditorOptions> {
-    if (this.loadingStatus === NzCodeEditorLoadingStatus.LOADED) {
+    if (loadingStatus === NzCodeEditorLoadingStatus.LOADED) {
       this.onInit();
-      return observableOf(this.getLatestOption());
+      return of(this.getLatestOption());
     }
 
-    if (this.loadingStatus === NzCodeEditorLoadingStatus.UNLOAD) {
+    if (loadingStatus === NzCodeEditorLoadingStatus.UNLOAD) {
       if (this.config.useStaticLoading && typeof monaco === 'undefined') {
         warn(
           'You choose to use static loading but it seems that you forget ' +
@@ -87,7 +95,7 @@ export class NzCodeEditorService implements OnDestroy {
       }
     }
 
-    return this.loaded$.asObservable().pipe(
+    return loaded$.pipe(
       tap(() => this.onInit()),
       map(() => this.getLatestOption())
     );
@@ -99,11 +107,11 @@ export class NzCodeEditorService implements OnDestroy {
       return;
     }
 
-    if (this.loadingStatus === NzCodeEditorLoadingStatus.LOADING) {
+    if (loadingStatus === NzCodeEditorLoadingStatus.LOADING) {
       return;
     }
 
-    this.loadingStatus = NzCodeEditorLoadingStatus.LOADING;
+    loadingStatus = NzCodeEditorLoadingStatus.LOADING;
 
     const assetsRoot = this.config.assetsRoot;
     const vs = assetsRoot ? `${assetsRoot}/vs` : 'assets/vs';
@@ -112,25 +120,44 @@ export class NzCodeEditorService implements OnDestroy {
 
     loadScript.type = 'text/javascript';
     loadScript.src = `${vs}/loader.js`;
-    loadScript.onload = () => {
+
+    const onLoad = (): void => {
+      cleanup();
       windowAsAny.require.config({
         paths: { vs }
       });
       windowAsAny.require(['vs/editor/editor.main'], () => {
         this.onLoad();
       });
     };
-    loadScript.onerror = () => {
+
+    const onError = (): void => {
+      cleanup();
       throw new Error(`${PREFIX} cannot load assets of monaco editor from source "${vs}".`);
     };
 
+    const cleanup = (): void => {
+      // Caretaker note: we have to remove these listeners once the `<script>` is loaded successfully
+      // or not since the `onLoad` listener captures `this`, which will prevent the `NzCodeEditorService`
+      // from being garbage collected.
+      loadScript.removeEventListener('load', onLoad);
+      loadScript.removeEventListener('error', onError);
+      // We don't need to keep the `<script>` element within the `<body>` since JavaScript has
+      // been executed and Monaco is available globally. E.g. Webpack, always removes `<script>`
+      // elements after loading chunks (see its `LoadScriptRuntimeModule`).
+      this.document.documentElement.removeChild(loadScript);
+    };
+
+    loadScript.addEventListener('load', onLoad);
+    loadScript.addEventListener('error', onError);
+
     this.document.documentElement.appendChild(loadScript);
   }
 
   private onLoad(): void {
-    this.loadingStatus = NzCodeEditorLoadingStatus.LOADED;
-    this.loaded$.next(true);
-    this.loaded$.complete();
+    loadingStatus = NzCodeEditorLoadingStatus.LOADED;
+    loaded$.next(true);
+    loaded$.complete();
 
     tryTriggerFunc(this.config.onLoad)();
   }

components/code-editor/typings.ts

@@ -14,7 +14,7 @@ export type JoinedEditorOptions = EditorOptions | DiffEditorOptions;
 
 export type NzEditorMode = 'normal' | 'diff';
 
-export enum NzCodeEditorLoadingStatus {
+export const enum NzCodeEditorLoadingStatus {
   UNLOAD = 'unload',
   LOADING = 'loading',
   LOADED = 'LOADED'