EventListener
A TypeScript sourced event listener for efficient applications based on the subscribe-publish pattern, less than 900 bytes when minified and packs a surprising amount of power.
Features
- EventListener is TypeScript sourced, with some types addapted from React;
- 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
globalListenerto call them all at once when event is triggered; -
EventListener "should" be able to manage event options, especially
once, meaning that when the option istrue, 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.
Install
npm i @thednp/event-listener
CDN
<script src="https://cdn.jsdelivr.net/npm/@thednp/event-listener/dist/event-listener.js"></script>Use
import * as Listener from '@thednp/event-listener';
// execute a listener once
Listener.on(document, 'DOMContentLoaded', () => {
console.log('document is now loaded');
},
{ once: true },
);
// add a listener with `useCapture: false`
function handleMyClick(e: Listener.NativeEvent) {
if (e.target.tagName === 'button') {
e.preventDefault();
e.stopImmediatePropagation();
}
console.log('do something else instead');
}
Listener.on(document, 'click', handleMyClick, false);
// remove a listener, `EventListener` will get listener options from registry
Listener.off(document, 'click', handleMyClick);
// add listener to `window`, this listener has no name and cannot be removed
Listener.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 = Listener.registry['click'].get(document);
// returns
Map(1) {
Entries(Array) => [
0: {
key: handleMyClick() // listener
value: false // listener options
}
],
size: 1, // size of the Map
prototype: [Prototype(Object)]
}
// check if element has listener
if (documentClickListeners && documentClickListeners.has(handleMyClick)) {
// do something about it
}
// check if a listener is the one you're looking for
if (documentClickListeners) {
const [eventListener] = documentClickListeners;
if (eventListener === 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 the types for more consistent code:
import { on, FocusEventHandler } from '@thednp/event-listener';
const handleMyFocus: FocusEventHandler<HTMLInputElement> = (e) => {
console.log(e)
}
const myInput = document.querySelector('input') || document.createElement('input');
on(myInput, 'focus', handleMyFocus);For more advanced use, check out the demo, showcasing the EventListener usage with a demo component.
Run the tests suite
- Download the package from Github;
- unpack/unzip and open the folder with your editor;
- open your terminal and navigate to the root of the unpacked folder;
- run
npm installornpm update, takes a few minutes to download the Electron browser; - run
npm run cypressto open the Cypress console ORnpm run testto run the tests in headless mode.
License
EventListener is released under the MIT License.