Checking on the event the relatedTarget exists before setting its property

Fixes a bug where relatedTarget was undefined in Firefox

fixes #2024
closes #2025

CHANGELOG.md

@@ -55,6 +55,7 @@ CHANGELOG
 * @mmcc added the vjs-big-play-centered class ([view](https://github.com/videojs/video.js/pull/2293))
 * @thijstriemstra added a logged error when a plugin is missing ([view](https://github.com/videojs/video.js/pull/1931))
 * @gkatsev fixed the texttrackchange event and text track display for non-native tracks ([view](https://github.com/videojs/video.js/pull/2215))
+* @mischizzle fixed event.relatedTarget in Firefox ([view](https://github.com/videojs/video.js/pull/2025))
 
 --------------------
 

src/js/utils/events.js

@@ -238,9 +238,11 @@ export function fixEvent(event) {
     }
 
     // Handle which other element the event is related to
-    event.relatedTarget = event.fromElement === event.target ?
-      event.toElement :
-      event.fromElement;
+    if (!event.relatedTarget) {
+      event.relatedTarget = event.fromElement === event.target ?
+        event.toElement :
+        event.fromElement;
+    }
 
     // Stop the default browser action
     event.preventDefault = function () {

test/unit/events.test.js

@@ -219,3 +219,23 @@ test('should have a defaultPrevented property on an event that was prevent from
 
   Events.trigger(el, 'test');
 });
+
+test('should have relatedTarget correctly set on the event', function() {
+  expect(2);
+
+  var el1 = document.createElement('div'),
+      el2 = document.createElement('div'),
+      relatedEl = document.createElement('div');
+
+  Events.on(el1, 'click', function(e){
+    equal(e.relatedTarget, relatedEl, 'relatedTarget is set for all browsers when related element is set on the event');
+  });
+
+  Events.trigger(el1, { type:'click', relatedTarget:relatedEl });
+
+  Events.on(el2, 'click', function(e) {
+    equal(e.relatedTarget, null, 'relatedTarget is null when none is provided');
+  });
+
+  Events.trigger(el2, { type:'click', relatedTarget:undefined });
+});