From 71079ce47e974df4139fb7f93cca5cc4da237a9d Mon Sep 17 00:00:00 2001
From: Andrew Scott <atscott01@gmail.com>
Date: Fri, 14 Aug 2020 10:32:55 -0700
Subject: [PATCH] fix(common): Allow scrolling when browser supports scrollTo
 (#38468)

This commit fixes a regression from "fix(common): ensure
scrollRestoration is writable (#30630)" that caused scrolling to not
happen at all in browsers that do not support scroll restoration. The
issue was that `supportScrollRestoration` was updated to return `false`
if a browser did not have a writable `scrollRestoration`. However, the
previous behavior was that the function would return `true` if
`window.scrollTo` was defined. Every scrolling function in the
`ViewportScroller` used `supportScrollRestoration` and, with the update
in bb88c9fa3daac80086efbda951d81c159e3840f4, no scrolling would be
performed if a browser did not have writable `scrollRestoration` but
_did_ have `window.scrollTo`.

Note, that this failure was detected in the saucelabs tests. IE does not
support scroll restoration so IE tests were failing.

PR Close #38468
---
 packages/common/src/viewport_scroller.ts       | 14 +++++++++++---
 packages/common/test/viewport_scroller_spec.ts | 15 ++++++++++++---
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/packages/common/src/viewport_scroller.ts b/packages/common/src/viewport_scroller.ts
index 355b90ecc79d6..a7c9093426938 100644
--- a/packages/common/src/viewport_scroller.ts
+++ b/packages/common/src/viewport_scroller.ts
@@ -88,7 +88,7 @@ export class BrowserViewportScroller implements ViewportScroller {
    * @returns The position in screen coordinates.
    */
   getScrollPosition(): [number, number] {
-    if (this.supportScrollRestoration()) {
+    if (this.supportsScrolling()) {
       return [this.window.scrollX, this.window.scrollY];
     } else {
       return [0, 0];
@@ -100,7 +100,7 @@ export class BrowserViewportScroller implements ViewportScroller {
    * @param position The new position in screen coordinates.
    */
   scrollToPosition(position: [number, number]): void {
-    if (this.supportScrollRestoration()) {
+    if (this.supportsScrolling()) {
       this.window.scrollTo(position[0], position[1]);
     }
   }
@@ -110,7 +110,7 @@ export class BrowserViewportScroller implements ViewportScroller {
    * @param anchor The ID of the anchor element.
    */
   scrollToAnchor(anchor: string): void {
-    if (this.supportScrollRestoration()) {
+    if (this.supportsScrolling()) {
       const elSelected =
           this.document.getElementById(anchor) || this.document.getElementsByName(anchor)[0];
       if (elSelected) {
@@ -163,6 +163,14 @@ export class BrowserViewportScroller implements ViewportScroller {
       return false;
     }
   }
+
+  private supportsScrolling(): boolean {
+    try {
+      return !!this.window.scrollTo;
+    } catch {
+      return false;
+    }
+  }
 }
 
 function getScrollRestorationProperty(obj: any): PropertyDescriptor|undefined {
diff --git a/packages/common/test/viewport_scroller_spec.ts b/packages/common/test/viewport_scroller_spec.ts
index 510a24bad5b7f..006702e985038 100644
--- a/packages/common/test/viewport_scroller_spec.ts
+++ b/packages/common/test/viewport_scroller_spec.ts
@@ -15,21 +15,30 @@ describe('BrowserViewportScroller', () => {
   let windowSpy: any;
 
   beforeEach(() => {
-    windowSpy = jasmine.createSpyObj('window', ['history']);
-    windowSpy.scrollTo = 1;
+    windowSpy = jasmine.createSpyObj('window', ['history', 'scrollTo']);
     windowSpy.history.scrollRestoration = 'auto';
     documentSpy = jasmine.createSpyObj('document', ['getElementById', 'getElementsByName']);
     scroller = new BrowserViewportScroller(documentSpy, windowSpy, null!);
   });
 
   describe('setHistoryScrollRestoration', () => {
-    it('should not crash when scrollRestoration is not writable', () => {
+    function createNonWritableScrollRestoration() {
       Object.defineProperty(windowSpy.history, 'scrollRestoration', {
         value: 'auto',
         configurable: true,
       });
+    }
+
+    it('should not crash when scrollRestoration is not writable', () => {
+      createNonWritableScrollRestoration();
       expect(() => scroller.setHistoryScrollRestoration('manual')).not.toThrow();
     });
+
+    it('should still allow scrolling if scrollRestoration is not writable', () => {
+      createNonWritableScrollRestoration();
+      scroller.scrollToPosition([10, 10]);
+      expect(windowSpy.scrollTo as jasmine.Spy).toHaveBeenCalledWith(10, 10);
+    });
   });
 
   describe('scrollToAnchor', () => {