From 511f729b7ac5c922b2d2360f11dec36d47d1667e Mon Sep 17 00:00:00 2001
From: Brandon Casey <BrandonOCasey@users.noreply.github.com>
Date: Thu, 28 Mar 2019 18:19:07 -0400
Subject: [PATCH] perf(live-tracker): disable live tracker on IE11 when
 document is hidden (#5896)

Disable the live tracker on IE11 when the document is hidden to fix the slow down and eventual crashing of web pages on IE11.

After #5879 was completed, we noticed that live streams still have an issue. This is because the live tracker we have also uses setInterval. Unfortunately, just disabling setInterval in the live tracker was not enough. Instead, we decided the best course of action is to just disable the live tracker altogether.
---
 src/js/live-tracker.js | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/src/js/live-tracker.js b/src/js/live-tracker.js
index 9b79f4976..5eb3b75d2 100644
--- a/src/js/live-tracker.js
+++ b/src/js/live-tracker.js
@@ -1,5 +1,7 @@
 import Component from './component.js';
 import mergeOptions from './utils/merge-options.js';
+import document from 'global/document';
+import * as browser from './utils/browser.js';
 
 /* track when we are at the live edge, and other helpers for live playback */
 class LiveTracker extends Component {
@@ -13,6 +15,25 @@ class LiveTracker extends Component {
     this.reset_();
 
     this.on(this.player_, 'durationchange', this.handleDurationchange);
+
+    // we don't need to track live playback if the document is hidden,
+    // also, tracking when the document is hidden can
+    // cause the CPU to spike and eventually crash the page on IE11.
+    if (browser.IE_VERSION && 'hidden' in document && 'visibilityState' in document) {
+      this.on(document, 'visibilitychange', this.handleVisibilityChange);
+    }
+  }
+
+  handleVisibilityChange() {
+    if (this.player_.duration() !== Infinity) {
+      return;
+    }
+
+    if (document.hidden) {
+      this.stopTracking();
+    } else {
+      this.startTracking();
+    }
   }
 
   isBehind_() {