fix: remove deprecated .extend method

Using classes inheritance instead of the deprecated `.extend` method
will allow users of this library to upgrade VideoJS to version 8.

See silvermine/videojs-chromecast#152
and silvermine/videojs-chromecast#147.

Related to silvermine/videojs-chromecast#152, Related to silvermine/videojs-chromecast#147.

src/js/components/AirPlayButton.js

@@ -1,119 +1,6 @@
 'use strict';
 
-/**
- * The AirPlayButton module contains both the AirPlayButton class definition and the
- * function used to register the button as a Video.js Component.
- *
- * @module AirPlayButton
- */
-
-var hasAirPlayAPISupport = require('../lib/hasAirPlayAPISupport'),
-    AirPlayButton;
-
-/**
-* The Video.js Button class is the base class for UI button components.
-*
-* @external Button
-* @see {@link http://docs.videojs.com/Button.html|Button}
-*/
-
-/** @lends AirPlayButton.prototype */
-AirPlayButton = {
-
-   /**
-    * This class is a button component designed to be displayed in the player UI's control
-    * bar. It displays an Apple AirPlay selection list when clicked.
-    *
-    * @constructs
-    * @extends external:Button
-    */
-   constructor: function(player, options) {
-      this.constructor.super_.apply(this, arguments);
-
-      if (!hasAirPlayAPISupport()) {
-         this.hide();
-      }
-
-      this._reactToAirPlayAvailableEvents();
-
-      if (options.addAirPlayLabelToButton) {
-         this.el().classList.add('vjs-airplay-button-lg');
-
-         this._labelEl = document.createElement('span');
-         this._labelEl.classList.add('vjs-airplay-button-label');
-         this._labelEl.textContent = this.localize('AirPlay');
-
-         this.el().appendChild(this._labelEl);
-      } else {
-         this.controlText('Start AirPlay');
-      }
-   },
-
-   /**
-    * Overrides Button#buildCSSClass to return the classes used on the button element.
-    *
-    * @param {DOMElement} el
-    * @see {@link http://docs.videojs.com/Button.html#buildCSSClass|Button#buildCSSClass}
-    */
-   buildCSSClass: function() {
-      return 'vjs-airplay-button ' + this.constructor.super_.prototype.buildCSSClass();
-   },
-
-   /**
-    * Overrides Button#handleClick to handle button click events. AirPlay functionality is
-    * handled outside of this class, which should be limited to UI related logic. This
-    * function simply triggers an event on the player.
-    *
-    * @fires AirPlayButton#airPlayRequested
-    * @param {DOMElement} el
-    * @see {@link http://docs.videojs.com/Button.html#handleClick|Button#handleClick}
-    */
-   handleClick: function() {
-      this.player().trigger('airPlayRequested');
-   },
-
-   /**
-    * Gets the underlying DOMElement used by the player.
-    *
-    * @private
-    * @returns {DOMElement} either an <audio> or <video> tag, depending on the type of
-    * player
-    */
-   _getMediaEl: function() {
-      var playerEl = this.player().el();
-
-      return playerEl.querySelector('video, audio');
-   },
-
-   /**
-    * Binds a listener to the `webkitplaybacktargetavailabilitychanged` event, if it is
-    * supported, that will show or hide this button Component based on the availability
-    * of the AirPlay function.
-    *
-    * @private
-    */
-   _reactToAirPlayAvailableEvents: function() {
-      var mediaEl = this._getMediaEl(),
-          self = this;
-
-      if (!mediaEl || !hasAirPlayAPISupport()) {
-         return;
-      }
-
-      function onTargetAvailabilityChanged(event) {
-         if (event.availability === 'available') {
-            self.show();
-         } else {
-            self.hide();
-         }
-      }
-
-      mediaEl.addEventListener('webkitplaybacktargetavailabilitychanged', onTargetAvailabilityChanged);
-      this.on('dispose', function() {
-         mediaEl.removeEventListener('webkitplaybacktargetavailabilitychanged', onTargetAvailabilityChanged);
-      });
-   },
-};
+var hasAirPlayAPISupport = require('../lib/hasAirPlayAPISupport');
 
 /**
  * Registers the AirPlayButton Component with Video.js. Calls
@@ -142,8 +29,121 @@ AirPlayButton = {
  * @see http://docs.videojs.com/module-videojs.html#~registerPlugin
  */
 module.exports = function(videojs) {
-   var AirPlayButtonImpl;
 
-   AirPlayButtonImpl = videojs.extend(videojs.getComponent('Button'), AirPlayButton);
-   videojs.registerComponent('airPlayButton', AirPlayButtonImpl);
+   /**
+    * The AirPlayButton module contains both the AirPlayButton class definition and the
+    * function used to register the button as a Video.js Component.
+    *
+    * @module AirPlayButton
+    */
+
+   const ButtonComponent = videojs.getComponent('Button');
+
+   /**
+   * The Video.js Button class is the base class for UI button components.
+   *
+   * @external Button
+   * @see {@link http://docs.videojs.com/Button.html|Button}
+   */
+
+   /** @lends AirPlayButton.prototype */
+   class AirPlayButton extends ButtonComponent {
+
+      /**
+       * This class is a button component designed to be displayed in the
+       * player UI's control bar. It displays an Apple AirPlay selection
+       * list when clicked.
+       *
+       * @constructs
+       * @extends external:Button
+       */
+      constructor(player, options) {
+         super(player, options);
+
+         if (!hasAirPlayAPISupport()) {
+            this.hide();
+         }
+
+         this._reactToAirPlayAvailableEvents();
+
+         if (options.addAirPlayLabelToButton) {
+            this.el().classList.add('vjs-airplay-button-lg');
+
+            this._labelEl = document.createElement('span');
+            this._labelEl.classList.add('vjs-airplay-button-label');
+            this._labelEl.textContent = this.localize('AirPlay');
+
+            this.el().appendChild(this._labelEl);
+         } else {
+            this.controlText('Start AirPlay');
+         }
+      }
+
+      /**
+       * Overrides Button#buildCSSClass to return the classes used on the button element.
+       *
+       * @param {DOMElement} el
+       * @see {@link http://docs.videojs.com/Button.html#buildCSSClass|Button#buildCSSClass}
+       */
+      buildCSSClass() {
+         return 'vjs-airplay-button ' + super.buildCSSClass();
+      }
+
+      /**
+       * Overrides Button#handleClick to handle button click events. AirPlay
+       * functionality is handled outside of this class, which should be limited
+       * to UI related logic. This function simply triggers an event on the player.
+       *
+       * @fires AirPlayButton#airPlayRequested
+       * @param {DOMElement} el
+       * @see {@link http://docs.videojs.com/Button.html#handleClick|Button#handleClick}
+       */
+      handleClick() {
+         this.player().trigger('airPlayRequested');
+      }
+
+      /**
+       * Gets the underlying DOMElement used by the player.
+       *
+       * @private
+       * @returns {DOMElement} either an <audio> or <video> tag, depending on the type of
+       * player
+       */
+      _getMediaEl() {
+         var playerEl = this.player().el();
+
+         return playerEl.querySelector('video, audio');
+      }
+
+      /**
+       * Binds a listener to the `webkitplaybacktargetavailabilitychanged` event, if it is
+       * supported, that will show or hide this button Component based on the availability
+       * of the AirPlay function.
+       *
+       * @private
+       */
+      _reactToAirPlayAvailableEvents() {
+         var mediaEl = this._getMediaEl(),
+             self = this;
+
+         if (!mediaEl || !hasAirPlayAPISupport()) {
+            return;
+         }
+
+         function onTargetAvailabilityChanged(event) {
+            if (event.availability === 'available') {
+               self.show();
+            } else {
+               self.hide();
+            }
+         }
+
+         mediaEl.addEventListener('webkitplaybacktargetavailabilitychanged', onTargetAvailabilityChanged);
+         this.on('dispose', function() {
+            mediaEl.removeEventListener('webkitplaybacktargetavailabilitychanged', onTargetAvailabilityChanged);
+         });
+      }
+   }
+
+   videojs.registerComponent('airPlayButton', AirPlayButton);
 };