fix: anchor links not scrolling into view (angular#519)

* Currently if someone visits a link that contains a fragment that refers to an anchor element, the element won't be scrolled into view properly. This is because the `focusOnNavigation` calls `focus()` after the scroll into view. This causes the focused element to be visible in view.
* Removes an unnecessary workaround for fixing fragment URLs.

Fixes angular#396

src/app/pages/component-viewer/component-api.html

@@ -1,10 +1,13 @@
-<span class="cdk-visually-hidden" tabindex="-1" #intialFocusTarget>
+<span class="cdk-visually-hidden" tabindex="-1" #initialFocusTarget>
   API for {{componentViewer.componentDocItem.id}}
 </span>
+
 <doc-viewer
-  documentUrl="/assets/documents/api/{{componentViewer.componentDocItem.packageName}}-{{componentViewer.componentDocItem.id}}.html"
-  class="docs-component-view-text-content docs-component-api"
-  (contentLoaded)="onContentLoaded()"></doc-viewer>
+    documentUrl="/assets/documents/api/{{componentViewer.componentDocItem.packageName}}-{{componentViewer.componentDocItem.id}}.html"
+    class="docs-component-view-text-content docs-component-api"
+    (contentRendered)="scrollToSelectedContentSection()">
+</doc-viewer>
+
 <table-of-contents #toc
     *ngIf="showToc | async"
     headerSelectors=".docs-api-h3,.docs-api-h4"

src/app/pages/component-viewer/component-examples.html

@@ -1,4 +1,4 @@
-<span class="cdk-visually-hidden" tabindex="-1" #intialFocusTarget>
+<span class="cdk-visually-hidden" tabindex="-1" #initialFocusTarget>
   Examples for {{componentViewer.componentDocItem.id}}
 </span>
 <example-viewer

src/app/pages/component-viewer/component-overview.html

@@ -1,9 +1,9 @@
-<span class="cdk-visually-hidden" tabindex="-1" #intialFocusTarget>
+<span class="cdk-visually-hidden" tabindex="-1" #initialFocusTarget>
   Overview for {{componentViewer.componentDocItem.id}}
 </span>
 <doc-viewer
     documentUrl="/assets/documents/overview/{{componentViewer.componentDocItem.packageName}}-{{componentViewer.componentDocItem.id}}.html"
     class="docs-component-view-text-content docs-component-overview"
-    (contentLoaded)="onContentLoaded()">
+    (contentRendered)="scrollToSelectedContentSection()">
 </doc-viewer>
 <table-of-contents #toc container=".mat-drawer-content" *ngIf="showToc | async"></table-of-contents>

src/app/pages/component-viewer/component-viewer.ts

@@ -65,7 +65,7 @@ export class ComponentViewer implements OnDestroy {
   encapsulation: ViewEncapsulation.None,
 })
 export class ComponentOverview implements OnInit {
-  @ViewChild('intialFocusTarget') focusTarget: ElementRef;
+  @ViewChild('initialFocusTarget') focusTarget: ElementRef;
   @ViewChild('toc') tableOfContents: TableOfContents;
   showToc: Observable<boolean>;
 
@@ -76,10 +76,10 @@ export class ComponentOverview implements OnInit {
 
   ngOnInit() {
     // 100ms timeout is used to allow the page to settle before moving focus for screen readers.
-    setTimeout(() => this.focusTarget.nativeElement.focus(), 100);
+    setTimeout(() => this.focusTarget.nativeElement.focus({preventScroll: true}), 100);
   }
 
-  onContentLoaded() {
+  scrollToSelectedContentSection() {
     if (this.tableOfContents) {
       this.tableOfContents.updateScrollPosition();
     }

src/app/pages/guide-viewer/guide-viewer.html

@@ -5,7 +5,7 @@ <h1>{{guide.name}}</h1>
 <div class="docs-guide-wrapper">
   <div class="docs-guide-toc-and-content">
     <doc-viewer class="docs-guide-content" 
-      (contentLoaded)="toc.updateScrollPosition()"
+      (contentRendered)="toc.updateScrollPosition()"
       [documentUrl]="guide.document"></doc-viewer>
     <table-of-contents #toc container="guide-viewer"></table-of-contents>
   </div>

src/app/shared/doc-viewer/doc-viewer.ts

@@ -8,12 +8,13 @@ import {
   EventEmitter,
   Injector,
   Input,
+  NgZone,
   OnDestroy,
   Output,
   ViewContainerRef,
 } from '@angular/core';
-import {Router} from '@angular/router';
 import {Subscription} from 'rxjs';
+import {take} from 'rxjs/operators';
 import {ExampleViewer} from '../example-viewer/example-viewer';
 import {HeaderLink} from './header-link';
 
@@ -31,7 +32,7 @@ export class DocViewer implements OnDestroy {
     this._fetchDocument(url);
   }
 
-  @Output() contentLoaded = new EventEmitter<void>();
+  @Output() contentRendered = new EventEmitter<void>();
 
   /** The document text. It should not be HTML encoded. */
   textContent = '';
@@ -42,7 +43,8 @@ export class DocViewer implements OnDestroy {
               private _http: HttpClient,
               private _injector: Injector,
               private _viewContainerRef: ViewContainerRef,
-              private _router: Router) {}
+              private _ngZone: NgZone) {
+  }
 
   /** Fetch a document by URL. */
   private _fetchDocument(url: string) {
@@ -66,8 +68,13 @@ export class DocViewer implements OnDestroy {
     this.textContent = this._elementRef.nativeElement.textContent;
     this._loadComponents('material-docs-example', ExampleViewer);
     this._loadComponents('header-link', HeaderLink);
-    this._fixFragmentUrls();
-    this.contentLoaded.next();
+
+    // Resolving and creating components dynamically in Angular happens synchronously, but since
+    // we want to emit the output if the components are actually rendered completely, we wait
+    // until the Angular zone becomes stable.
+    this._ngZone.onStable
+      .pipe(take(1))
+      .subscribe(() => this.contentRendered.next());
   }
 
   /** Show an error that occurred when fetching a document. */
@@ -77,15 +84,6 @@ export class DocViewer implements OnDestroy {
       `Failed to load document: ${url}. Error: ${error.statusText}`;
   }
 
-  releadLiveExamples() {
-    // When the example viewer is dynamically loaded inside of md-tabs, they somehow end up in
-    // the wrong place in the DOM after switching tabs. This function is a workaround to
-    // put the live examples back in the right place.
-    this._clearLiveExamples();
-    this._loadComponents('material-docs-example', ExampleViewer);
-    this._loadComponents('header-link', HeaderLink);
-  }
-
   /** Instantiate a ExampleViewer for each example. */
   private _loadComponents(componentName: string, componentClass: any) {
     let exampleElements =
@@ -108,25 +106,6 @@ export class DocViewer implements OnDestroy {
     this._portalHosts = [];
   }
 
-  /**
-   * A fragment link is a link that references a specific element on the page that should be
-   * scrolled into the viewport on page load or click.
-   *
-   * By default those links refer to the root page of the documentation and the fragment links
-   * won't work properly. Those links need to be updated to be relative to the current base URL.
-   */
-  private _fixFragmentUrls() {
-    const baseUrl = this._router.url.split('#')[0];
-    const anchorElements =
-      [].slice.call(this._elementRef.nativeElement.querySelectorAll('a')) as HTMLAnchorElement[];
-
-    // Update hash links that are referring to the same page and host. Links that are referring
-    // to a different destination shouldn't be updated. For example the Google Fonts URL.
-    anchorElements
-      .filter(anchorEl => anchorEl.hash && anchorEl.host === location.host)
-      .forEach(anchorEl => anchorEl.href = `${baseUrl}${anchorEl.hash}`);
-  }
-
   ngOnDestroy() {
     this._clearLiveExamples();
 

src/app/shared/doc-viewer/header-link.ts

@@ -1,4 +1,4 @@
-import {Component, Input, OnInit} from '@angular/core';
+import {Component, Input} from '@angular/core';
 import {Router} from '@angular/router';
 
 /**
@@ -19,27 +19,31 @@ import {Router} from '@angular/router';
   template: `
     <a
       title="Link to this heading"
-      [attr.aria-describedby]="example"
-      class="docs-markdown-a"
       aria-label="Link to this heading"
-      [href]="url">
+      class="docs-markdown-a"
+      [attr.aria-describedby]="example"
+      [href]="_getFragmentUrl()">
       <mat-icon>link</mat-icon>
     </a>
   `
 })
-export class HeaderLink implements OnInit {
+export class HeaderLink {
 
+  /**
+   * Id of the anchor element. Note that is uses "example" because we instantiate the
+   * header link components through the ComponentPortal.
+   */
   @Input() example: string;
 
-  url: string;
-  private _rootUrl: string;
+  /** Base URL that is used to build an absolute fragment URL. */
+  private _baseUrl: string;
 
   constructor(router: Router) {
-    this._rootUrl = router.url.split('#')[0];
+    this._baseUrl = router.url.split('#')[0];
   }
 
-  ngOnInit(): void {
-    this.url = `${this._rootUrl}#${this.example}`;
+  _getFragmentUrl(): string {
+    return `${this._baseUrl}#${this.example}`;
   }
 
 }

src/app/shared/navigation-focus/navigation-focus.ts

@@ -13,7 +13,7 @@ export class NavigationFocus implements OnInit {
   ngOnInit() {
     clearTimeout(lastTimeoutId);
     // 100ms timeout is used to allow the page to settle before moving focus for screen readers.
-    lastTimeoutId = setTimeout(() => this.el.nativeElement.focus(), 100);
+    lastTimeoutId = setTimeout(() => this.el.nativeElement.focus({preventScroll: true}), 100);
   }
 }