perf: fix an event target memory leak (#5855)

src/js/event-target.js

@@ -138,6 +138,11 @@ EventTarget.prototype.one = function(type, fn) {
 EventTarget.prototype.trigger = function(event) {
   const type = event.type || event;
 
+  // deprecation
+  // In a future version we should default target to `this`
+  // similar to how we default the target to `elem` in
+  // `Events.trigger`. Right now the default `target` will be
+  // `document` due to the `Event.fixEvent` call.
   if (typeof event === 'string') {
     event = {type};
   }

src/js/tracks/track-list.js

@@ -72,7 +72,8 @@ class TrackList extends EventTarget {
        */
       this.trigger({
         track,
-        type: 'addtrack'
+        type: 'addtrack',
+        target: this
       });
     }
   }
@@ -115,7 +116,8 @@ class TrackList extends EventTarget {
      */
     this.trigger({
       track,
-      type: 'removetrack'
+      type: 'removetrack',
+      target: this
     });
   }
 

src/js/utils/events.js

@@ -431,7 +431,7 @@ export function trigger(elem, event, hash) {
     trigger.call(null, parent, event, hash);
 
   // If at the top of the DOM, triggers the default action unless disabled.
-  } else if (!parent && !event.defaultPrevented) {
+  } else if (!parent && !event.defaultPrevented && event.target && event.target[event.type]) {
     const targetData = DomData.getData(event.target);
 
     // Checks if the target has a default action for this event.