event-listener-extended

A wrapper to EventTarget.addEventListener that supports multiple targets, event names and delegated events with a convenient remove listener mechanism.

Installation

npm install event-listener-extended --save

Examples

Basic usage

Set target, event and callback which are the required options.

import { addListener } from 'event-listener-extended';

const list = document.getElementById('list');

const removeListener = addListener({
  target: list,
  event: 'click',
  callback(e) {
    console.log(`x: ${e.clientX}, y: ${e.clientY}`)
  }
});

// Call when cleaning up
removeListener();

Once

Use the once option to listen to an event only once.

import { addListener } from 'event-listener-extended';

const list = document.getElementById('list');

const removeListener = addListener({
  target: list,
  event: 'pointermove',
  callback(e) {
    console.log(`x: ${e.clientX}, y: ${e.clientY}`)
  },
  once: true,
});

Multiple events

Listen to multiple events by setting an array or a string of space-separated event names as the event option.

import { addListener } from 'event-listener-extended';

const list = document.getElementById('list');

const removeListener = addListener({
  target: list,
  event: ['pointerdown', 'pointerup'],
  callback(e) {
    console.log(`${e.type}: x: ${e.clientX}, y: ${e.clientY}`)
  }
});

// Call when cleaning up
removeListener();

Multiple targets

Listen to multiple targets by setting EventTarget[] or NodeListOf<EventTarget> as the target option.

import { addListener } from 'event-listener-extended';

const list = document.getElementById('list');

const removeListener = addListener({
  target: list.getElementsByTagName('li'),
  event: 'click',
  callback(e) {
    console.log(`x: ${e.clientX}, y: ${e.clientY}`)
  }
});

// Call when cleaning up
removeListener();

Under the hood, .addEventListener() will be called for each node in the target NodeList

A delegated listener

A delegated listener is a pseudo-listener that is bound to a common ancestor of targeted nodes rather than the targeted nodes themselves. This allows to bind the event only once, to the ancestor target (i.e. list element) without having to add / remove the listener when a new node (i.e. list item) is added / removed.

Event delegation is enabled by using delegateSelector option - which must be a CSS selector that targeted items will match.

import { addListener } from 'event-listener-extended';

const list = document.getElementById('list');

const removeListener = addListener({
  target: container,
  event: 'click',
  callback(e) {
    console.log(this.tagName); // LI
  },
  delegateSelector: 'li',
});

// Clicking this newly added item will fire the listener without having to add a listener on it
const li = document.createElement('li');
list.appendChild(li);

// Call when cleaning up
removeListener();

Mind that delegated listeners add extra processing overhead on the event to find the matched node, thus are not recommended for events that fire often like pointermove, pointerin.

Options

See the Options interface in this file for the full list of options.