code: function once(element) {
  	  var _this2 = this;
  
  	  var events = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : '';
  	  var callback = arguments.length > 2 ? arguments[2] : undefined;
  	  var passive = arguments.length > 3 && arguments[3] !== undefined ? arguments[3] : true;
  	  var capture = arguments.length > 4 && arguments[4] !== undefined ? arguments[4] : false;
  
  	  var onceCallback = function onceCallback() {
  	    off(element, events, onceCallback, passive, capture);
  
  	    for (var _len = arguments.length, args = new Array(_len), _key = 0; _key < _len; _key++) {
  	      args[_key] = arguments[_key];
  	    }
  
  	    callback.apply(_this2, args);
  	  };
  
  	  toggleListener.call(this, element, events, onceCallback, true, passive, capture);
  	}
docs: Bind once-only event handler