From c26e1bba1d1eb30b4592bc30f68c6acaa8cc5bd4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matias=20Niemel=C3=A4?= <matias@yearofmoo.com>
Date: Mon, 27 Nov 2017 14:40:09 -0800
Subject: [PATCH] fix(animations): ensure the web-animations driver properly
 handles empty keyframes (#20648)

Closes #15858

PR Close #20648
---
 .../web_animations/web_animations_player.ts    |  2 +-
 .../web_animations_player_spec.ts              | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/packages/animations/browser/src/render/web_animations/web_animations_player.ts b/packages/animations/browser/src/render/web_animations/web_animations_player.ts
index 879bcf3f1d..56e5a2ea0f 100644
--- a/packages/animations/browser/src/render/web_animations/web_animations_player.ts
+++ b/packages/animations/browser/src/render/web_animations/web_animations_player.ts
@@ -65,7 +65,7 @@ export class WebAnimationsPlayer implements AnimationPlayer {
 
     const keyframes = this.keyframes.map(styles => copyStyles(styles, false));
     const previousStyleProps = Object.keys(this.previousStyles);
-    if (previousStyleProps.length) {
+    if (previousStyleProps.length && keyframes.length) {
       let startingKeyframe = keyframes[0];
       let missingStyleProps: string[] = [];
       previousStyleProps.forEach(prop => {
diff --git a/packages/animations/browser/test/render/web_animations/web_animations_player_spec.ts b/packages/animations/browser/test/render/web_animations/web_animations_player_spec.ts
index 0fd04c8977..139aecfcf4 100644
--- a/packages/animations/browser/test/render/web_animations/web_animations_player_spec.ts
+++ b/packages/animations/browser/test/render/web_animations/web_animations_player_spec.ts
@@ -33,6 +33,24 @@ export function main() {
       expect(p.log).toEqual(['pause', 'play']);
     });
 
+    it('should allow an empty set of keyframes with a set of previous styles', () => {
+      const previousKeyframes = [
+        {opacity: 0, offset: 0},
+        {opacity: 1, offset: 1},
+      ];
+
+      const previousPlayer = new WebAnimationsPlayer(element, previousKeyframes, {duration: 1000});
+      previousPlayer.play();
+      previousPlayer.finish();
+      previousPlayer.beforeDestroy();
+
+      const EMPTY_KEYFRAMES: any[] = [];
+      const player =
+          new WebAnimationsPlayer(element, EMPTY_KEYFRAMES, {duration: 1000}, [previousPlayer]);
+      player.play();
+      player.destroy();
+    });
+
     it('should not pause the player if created and started before initialized', () => {
       const keyframes = [
         {opacity: 0, offset: 0},