feat: optimize code

Signed-off-by: SuZhou-Joe <[email protected]>

src/core/public/chrome/chrome_service.test.ts

@@ -314,7 +314,6 @@ describe('start', () => {
           false,
           true,
           true,
-          true,
         ]
       `);
     });

src/core/public/chrome/chrome_service.tsx

@@ -41,7 +41,7 @@ import {
   ReplaySubject,
   Subscription,
 } from 'rxjs';
-import { flatMap, map, takeUntil } from 'rxjs/operators';
+import { map, switchMap, takeUntil } from 'rxjs/operators';
 import { EuiLink } from '@elastic/eui';
 import { mountReactNode } from '../utils/mount';
 import { InternalApplicationStart } from '../application';
@@ -160,32 +160,25 @@ export class ChromeService {
     const isEmbedded = new URL(location.hash.slice(1), location.origin).searchParams.has('embed');
     this.isForceHidden$ = new BehaviorSubject(isEmbedded);
 
-    /**
-     * There is a staled closure issue here.
-     * For example, when currentAppId$ is going through A -> B -> C and
-     * the application.applications$ just get changed in B, then it will always use B as the currentAppId
-     * even though the latest appId now is C.
-     */
-    let currentAppId: string | undefined;
-
     const appHidden$ = merge(
       // For the isVisible$ logic, having no mounted app is equivalent to having a hidden app
       // in the sense that the chrome UI should not be displayed until a non-chromeless app is mounting or mounted
       of(true),
       application.currentAppId$.pipe(
-        flatMap((appId) => {
-          // Update the currentAppId to latest
-          currentAppId = appId;
-          return application.applications$.pipe(
-            map((applications) => {
-              return (
-                !!currentAppId &&
-                applications.has(currentAppId) &&
-                !!applications.get(currentAppId)!.chromeless
-              );
-            })
-          );
-        })
+        /**
+         * There is a staled closure issue here.
+         * For example, when currentAppId$ is going through A -> B -> C and
+         * the application.applications$ just get changed in B, then it will always use B as the currentAppId
+         * even though the latest appId now is C.
+         */
+        switchMap((appId) =>
+          application.applications$.pipe(
+            map(
+              (applications) =>
+                !!appId && applications.has(appId) && !!applications.get(appId)!.chromeless
+            )
+          )
+        )
       )
     );
     this.isVisible$ = combineLatest([appHidden$, this.isForceHidden$]).pipe(
@@ -198,7 +191,7 @@ export class ChromeService {
     this.headerVariantOverride$ = new BehaviorSubject<HeaderVariant | undefined>(undefined);
 
     const appHeaderVariant$ = application.currentAppId$.pipe(
-      flatMap((appId) =>
+      switchMap((appId) =>
         application.applications$.pipe(
           map(
             (applications) =>