code: function () {
          var dom = this.domElement;
  
          vendor.addEventListener(dom, 'touchstart', this._mouseDownHandler);
  
          vendor.addEventListener(dom, 'mousedown', this._mouseDownHandler);
          vendor.addEventListener(dom, 'wheel', this._mouseWheelHandler);
  
          if (this.timeline) {
              this.timeline.on('frame', this.update, this);
          }
          if (this.target) {
              this.decomposeTransform();
          }
      }
docs: Initialize.
  Mouse event binding