delegate-event-listener

Delegate event listener.

Features:

• Flexible usage with native addEventListener and removeEventListener
• Current target reference with event.delegateTarget property
• Prevents listener triggering if target element is inside form [disabled] element
• Handles delegating of non-delegated events such as focus, blur, mouseenter/leave, pointerenter/leave

Install

npm install delegate-event-listener --save

Usage

Given following markup and JS functionality clicking only on #frankie will trigger event listener even though event handler is attached on #jackie.

<div id="jackie">
	<div id="frankie">Frankie</div>
	<div id="sally">Sally</div>
</div>

import delegate from 'delegate-event-listener';

const element = document.querySelector('#jackie');

element.addEventListener(
	'click',
	delegate('#frankie', (e) => {
		// e.delegateTarget === document.querySelector('#frankie')
		// Clicked on #frankie!
	})
);

// Delegating non-delegated events such as `focus` is achieved with alternative function output
element.addEventListener(
	...delegate('focus', '#frankie', (e) => {
		// e.delegateTarget === document.querySelector('#frankie')
		// Clicked on #frankie!
	})
);

API

delegate([eventName, ]selector, listener)

Returns: Function|array

Delegated function.

If delegate function call contains 3 arguments, first argument is event name which will then be used to resolve proper delegated event. Array of values is then returned, first argument being event name used to fix event (e.g. mouseover for mouseenter), and second argument being event handler. Those values should then be applied to addEventListener (either via spreading or manual assignment).

Original event (one which was supplied to function) is available as event.originalEventType. Resolved event is available to native event.type:

eventName

Type: string

Event name. Used only for alternative function output. Event will be mapped to proper delegatable event (e.g. mouseenter for mouseover).

selector

Type: string

CSS selector whose ancestor is element on which event handler is attached. If it’s empty string, event handler will be attached to element which called addEventListener.

listener

Type: Function

Event listener for event handler.

Native Event object is decorated with event.delegateTarget property. This property is same as node resolved from selector. event.currentTarget is equal to node on which event listener is attached.

For non-delegated event handlers attached directly to an element, event.delegateTarget will always be equal to event.currentTarget.

FAQ

Triggering custom event doesn’t run listener function

Event propagation in Event constructor is not active by default. You have to explicitly enable it.

document.body.addEventListener(
	'click',
	delegate('button', () => {
		// …
	})
);

// Setting `bubbles: true` makes event propagation active
document
	.querySelector('button')
	.dispatchEvent(new Event('click', { bubbles: true }));

Browser support

Tested in IE9+ and all modern browsers.

Test

For automated tests, run npm run test:automated (append :watch for watcher support).

License

MIT © Ivan Nikolić