code: function(val) {
      var self = this;
  
      // Update the global volume (affecting all Howls).
      Howler.volume(val);
  
      // Update the display on the slider.
      var barWidth = (val * 90) / 100;
      barFull.style.width = (barWidth * 100) + '%';
      sliderBtn.style.left = (window.innerWidth * barWidth + window.innerWidth * 0.05 - 25) + 'px';
    }
docs: Set the volume and update the volume slider display.
  @param  {Number} val Volume between 0 and 1.