feat: add isDisposed method to components (#6099)

docs/guides/player-workflows.md

@@ -54,6 +54,10 @@ Additionally, these actions are recursively applied to _all_ the player's child
 
 > **Note**: Do _not_ remove players via standard DOM removal methods: this will leave listeners and other objects in memory that you might not be able to clean up!
 
+### Checking if a Player is Disposed
+
+At times, it is useful to know whether or not a player reference in your code is stale. The `isDisposed()` method is available on all components (including players) for this purpose.
+
 ### Signs of an Undisposed Player
 
 Seeing an error such as:

src/js/component.js

@@ -58,6 +58,8 @@ class Component {
       this.player_ = player;
     }
 
+    this.isDisposed_ = false;
+
     // Hold the reference to the parent component via `addChild` method
     this.parentComponent_ = null;
 
@@ -124,18 +126,25 @@ class Component {
    */
   dispose() {
 
+    // Bail out if the component has already been disposed.
+    if (this.isDisposed_) {
+      return;
+    }
+
     /**
      * Triggered when a `Component` is disposed.
      *
      * @event Component#dispose
      * @type {EventTarget~Event}
      *
      * @property {boolean} [bubbles=false]
-     *           set to false so that the close event does not
+     *           set to false so that the dispose event does not
      *           bubble up
      */
     this.trigger({type: 'dispose', bubbles: false});
 
+    this.isDisposed_ = true;
+
     // Dispose all children.
     if (this.children_) {
       for (let i = this.children_.length - 1; i >= 0; i--) {
@@ -168,6 +177,16 @@ class Component {
     this.player_ = null;
   }
 
+  /**
+   * Determine whether or not this component has been disposed.
+   *
+   * @return {boolean}
+   *         If the component has been disposed, will be `true`. Otherwise, `false`.
+   */
+  isDisposed() {
+    return Boolean(this.isDisposed_);
+  }
+
   /**
    * Return the {@link Player} that the `Component` has attached to.
    *

test/unit/component.test.js

@@ -340,6 +340,7 @@ QUnit.test('should dispose of component and children', function(assert) {
   const child = comp.addChild('Component');
 
   assert.ok(comp.children().length === 1);
+  assert.notOk(comp.isDisposed(), 'the component reports that it is not disposed');
 
   // Add a listener
   comp.on('click', function() {
@@ -370,6 +371,7 @@ QUnit.test('should dispose of component and children', function(assert) {
     !Object.getOwnPropertyNames(data).length,
     'original listener data object was emptied'
   );
+  assert.ok(comp.isDisposed(), 'the component reports that it is disposed');
 });
 
 QUnit.test('should add and remove event listeners to element', function(assert) {