Allow objects as event handlers

[[email protected]…]

Doing OOP with jQuery events requires a lot of $.proxy boilerplate. the .addEventListener interface allows passing an object as a handler like so:

function SomeWidget( elem ) {
	this.elem = elem;
}

SomeWidget.prototype = {
	constructor: SomeWidget,

	renderTo: function( target ) {
		$(target).append(this.elem);
		this.elem.addEventListener( "click", this );
		this.elem.addEventListener( "mousemove", this );
	},

	mousemove: function( e ) {

	},

	click: function( e ) {

	},

	handleEvent: function( e ) {
		return this[e.type].apply( this, arguments );
	}
};

With jQuery you have to do this:

function SomeWidget( elem ) {
	this.elem = elem;
	//Each method needs to be bound to the instance. This also has overhead of creating many functions.
	this.mousemove = $.proxy( this.mousemove, this );
	this.click = $.proxy( this.click, this );
}

SomeWidget.prototype = {
	constructor: SomeWidget,

	renderTo: function( target ) {
		$(target).append(this.elem);
		$(this.elem).on( {
			click: this.click,
			mousemove: this.mousemove
		});
	},

	mousemove: function( e ) {

	},

	click: function( e ) {

	}
};

With jQuery supporting objects as event handlers, it would work like:

function SomeWidget( elem ) {
	this.elem = elem;
}

SomeWidget.prototype = {
	constructor: SomeWidget,

	renderTo: function( target ) {
		$(target).append(this.elem);
		$(this.elem).on( "click mousemove", this );
	},

	mousemove: function( e ) {

	},

	click: function( e ) {

	},

	handleEvent: function( e ) {
		return this[e.type].apply( this, arguments );
	}
};

And that's it. No $.proxy hacks, no redundant creation of functions just to retain binding.

[dmethvin]

Worth thinking about so I'll leave it open.

[Rick Waldron]

I'm into this

​http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-EventListener

@dmethvin - if you don't mind, I'd like to prototype this one :)

[Rick Waldron]

note to self...

 .on({ click: fn }) 

Has to support handling:

// delegated events
.on({ click: fn }, "div");

// data object events
.on({ click: fn }, "div", dataobject);

[dmethvin]

Bulk change from enhancement to feature.

[dmethvin]

gnarf and I talked about this in Austin. It would be a very low-level public interface, ideally the current event features would be built on top of it. Essentially replace ​this function so we don't go to the current jQuery dispatcher and instead use a caller-supplied dispatching object. That would provide users with low-overhead ways to handle high-frequency events like scroll or mousemove (or the upcoming pointermove) by avoiding jQuery.event.fix() for example.

[gibson042]

A good implementation would make something like ​https://github.com/jquery/jquery/pull/1367/files significantly more lightweight.

[dmethvin]

Additional note re #14953, can we have a way to do capturing here? As I understand the .addEventListener interface it seems like all the events in the attached object would be capturing.

[[email protected]…]

In addEventListener the optional useCapture parameter defines whether capturing is in use regardless if you use a function or an object as a handler. The default is false so in the example all events are bubbling.

[dmethvin]

Re rwaldron's comment 5 above, I am thinking this interface will be low level enough that we will not support any type of enhancement. That includes special events, delegation, fixing, or additional data. To get those things you'll either need to do them yourself or use the standard interfaces.

For the additional data issue, it's probably not an issue since the this points to an object you get to populate. The other features cost execution time and one of the reasons for this interface is to provide a clean way to get performance when you don't need things like event normalization across browsers.

[m_gol]

Migrated to ​https://github.com/jquery/jquery/issues/1735