Triggering jQuery and vanilla JS events

3 Jul 2015 · by David DeSandro

You can now bind to jQuery events in Isotope, Packery, and Masonry. The recent upgrades allow you to use standard jQuery event methods .on(), .off, and .one(), rather than using ugly plugin method syntax.

// previous plugin method syntax
// Isotope <= v2.2.0
$grid.isotope( 'on', 'layoutComplete', function() {...})

// standard jQuery event
// Isotope >= v2.2.1
$grid.on( 'layoutComplete', function() {...})

View Isotope layoutComplete demo on CodePen.

This feature is already in Flickity and Draggabilly. It was prime time to port it over to the layout libraries.

jQuery plugin events

Events are a great API design pattern to add to any library. They enable developers to build functionality on top of a library, without having to add lots of code into a big config object. Take a look at this Draggabilly demo, which disables other draggables so that only one can be dragged at a time.

var $draggable = $('.draggable').draggabilly();

// disable other draggabillies on dragStart
$draggable.on( 'dragStart', function( event ) {
  $draggable.filter( function( i, elem ) {
    return elem != event.target;
  }).draggabilly('disable');
});
// re-enable on dragEnd
$draggable.on( 'dragEnd', function() {
  $draggable.draggabilly('enable');
});

Unfortunately, events are often missing from jQuery plugins. Many plugins stick to the config object pattern for this kind of logic. Here's that same code block re-written using a config object.

var $draggable = $('.draggable').draggabilly({
  onDragStart: function( event ) {
    $draggable.filter( function( i, elem ) {
      return elem != event.target;
    }).draggabilly('disable');
  },
  onDragEnd: function() {
    $draggable.draggabilly('enable');
  }
});

While this code is more compact, it comes at a cost. Config objects make sense for settings. They align well with novice developers thinking declaratively, like writing HTML and CSS. But events are not settings. Events can be turned on and off asychronously. The same event can have multiple listeners. Events can require programmatic thinking. Using events and listeners can open up how to think like a programmer.

Consider a scenario where I want to bind to an event after one event has happened, or a scenario when I want to unbind an event.

$draggable.on( 'dragStart', function() {
  // listen to dragEnd after dragStart
  $draggable.on( 'dragEnd', onDragEnd );
});

function onDragEnd() {
  // on dragEnd after dragStart logic...
  // unbind listener
  $draggable.off( 'dragEnd', onDragEnd )
}

Re-writing this code with a config object pattern would look ugly. Using the event pattern makes for less complex code that's easier to follow. It exposes a different kind of programmatic logic that's not possible with declarative config objects.

dispatchEvent method

Looking under the hood, triggering jQuery and vanilla JS events is handled by the dispatchEvent method:

/**
 * emits events via eventEmitter and jQuery events
 * @param {String} type - name of event
 * @param {Event} event - original event
 * @param {Array} args - extra arguments
 */
Widget.prototype.dispatchEvent = function( type, event, args ) {
  // add original event to arguments
  var emitArgs = event ? [ event ].concat( args ) : args;
  // trigger vanilla JS event
  this.emitEvent( type, emitArgs );
  // trigger jQuery event
  if ( jQuery && this.$element ) {
    if ( event ) {
      // create jQuery event
      var $event = jQuery.Event( event );
      $event.type = type;
      this.$element.trigger( $event, args );
    } else {
      // just trigger with type if no event available
      this.$element.trigger( type, args );
    }
  }
};

dispatchEvent emits an event with EventEmitter for vanilla JS events, and creates and triggers a jQuery event. dispatchEvent is then used in the widget's logic:

// with Event object
this.dispatchEvent( 'eventName', event, [ arg1, arg2 ] );
// no Event object
this.dispatchEvent( 'eventName', null, [ arg1, arg2 ] );

Developers can then bind listeners with jQuery or vanilla JS.

// jQuery
$elem.on( 'eventName', function( event, arg1, arg2 ) {
  //...
})

// vanilla JS
widget.on( 'eventName', function( event, arg1, arg2 ) {
  //...
})

Adding jQuery events is a small feature, but it allows developers to re-use code patterns they are familiar with, which makes Metafizzy libraries more approachable. Compared to the previous syntax, a novice developer can look over event demo code and think "Yeah, I can do that."

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