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Author message:

event-listener.js is no longer maintained. Please use @thednp/event-listener

event-listener.js

EventListener

Modern event listener for efficient applications based on the subscribe-publish pattern.

EventListener is less than 900 bytes when minified, but packs a surprising amount of power.

Features

• EventListener is ES6+ sourced with TypeScript definitions;
• EventListener comes with ES6, ES5 and ESM packaging, all in /dist folder;
• EventListener makes use of the native Map to subscribe/register or unsubscribe/remove listeners, which is perfect since we need to make sure the exact listeners are added/removed; this completely invalidates the need to deconstruct function objects for comparison's sake to make sure event listeners are properly handled;
• EventListener allows you to register multiple listeners for the same target, even of the same type, but always uses a single globalListener to call them all at once when event is triggered;
• EventListener "should" be able to manage event options, especially once, meaning that when the option is true, the listener is automatically un-subscribed and detached from target;
• EventListener will unsubscribe and detach listeners with the same options used when attached, which means you can "lazy" remove listeners on the fly.

NPM

npm install event-listener.js

CDN

<script src="https://cdn.jsdelivr.net/npm/event-listener.js/dist/event-listener.min.js"></script>

Use

import EventListener from 'event-listener.js';

// execute a listener once
EventListener.on(document, 'DOMContentLoaded', () => {
  console.log('document is now loaded');
}, { once: true });


// add a listener with `useCapture: false`
function handleMyClick(e) {
  if (e.target.tagName === 'button') {
    e.preventDefault();
    e.stopImmediatePropagation();
  }
  console.log('do something else instead');
}
EventListener.on(document, 'click', handleMyClick, false);

// remove a listener, `EventListener` will get listener options from registry
EventListener.off(document, 'click', handleMyClick);

// add listener to `window`, this listener has no name and cannot be removed
EventListener.on(window, 'scroll', () => console.log(window.scrollY));

Since we're implementing Map, you can make use of its prototype to access registry:

// get element listener registry
const documentClickListeners = EventListener.registry['click'].get(document);

// returns
Map(1) {
  Entries(Array) => [
    0: {
      key: ƒ() // listener
      value: false // listener options
    }
  ],
  size: 1, // size of the Map
  prototype: Prototype
}

// check if element has listener
if (documentClickListeners && documentClickListeners.has(handleMyClick)) {
  // do something about it
}

// get listener options
const myListenerOptions = documentClickListeners && documentClickListeners.get(handleMyClick));

// returns false, which is the `useCapture` option value added for `handleMyClick`

Advanced Use

You can also make use of "tree shaking" to import only the module you want, for instance:

import { addListener } from 'event-listener.js';

addListener(document, handleMyClick, true);

For more advanced use, check out the demo, showcasing the EventListener usage with a demo component.

License

EventListener is released under the MIT License.