code: function(type, handler) {
  
  			var handlers = this._handlers[type],
  				i,
  				len;
  
  			if (typeof handlers === 'undefined') {
  				handlers = this._handlers[type] = [];
  			}
  
  			for (i = 0, len = handlers.length; i < len; i++) {
  				if (handlers[i] === handler) {
  					// prevent duplicate handlers
  					return;
  				}
  			}
  
  			handlers.push(handler);
  		}
docs: Adds a new event handler for a particular type of event.
  @param {string} type The name of the event to listen for.
  @param {Function} handler The function to call when the event occurs.
  @returns {void}