title: Write plugin for VideoJS 5
body: <p>When I trying to use the newest version of videojs 5, the following code is no longer worked. I am trying to write a videojs plugin, but videojs 5 use ecmascript 6, which is new to me. Any helps are appreciated.</p>
  
  <pre><code>   videojs.SharingButton = videojs.Button.extend({
      /** @constructor */
      init: function(player, options){
          videojs.Button.call(this, player, options);
          this.player = player;
      }
  });
  
  videojs.SharingButton.prototype.createEl = function(tagName,options) {
      return videojs.Component.prototype.createEl(tagName,{
          className: this.buildCSSClass(),
          innerHTML: '',
          role: 'button',
          'aria-live': 'polite', // let the screen reader user know that the text of the button may change
          tabIndex: 0
      });
  }
  
  videojs.SharingButton.prototype.buttonText = 'Share Video';
  
  videojs.SharingButton.prototype.options_ = {};
  
  videojs.SharingButton.prototype.buildCSSClass = function(){
      return 'vjs-sharing-control ';
  };
  </code></pre>