Delegate

This is an event delegation library for the browser. The interface is similar to that of jQuery, making it easy to learn.

Installation

via npm:

npm i @knowledgecode/delegate

Usage

import delegate from '@knowledgecode/delegate';

ES Modules:

<script type="module">
  import delegate from '/path/to/esm/delegate.js';

  delegate(document).on('click', '#button', () => {
    alert('Clicked!');
  });
</script>

Traditional:

<script src="/path/to/umd/delegate.js"></script>
<script>
  delegate(document).on('click', '#button', () => {
    alert('Clicked!');
  });
</script>

API

delegate

Creates a delegate instance.

• {Object} baseEventTarget - A base element that receives events

const body = delegate(document.body);

const container = delegate(document.querySelector('.container'));

on

Registers an event listener.

• {string} eventName - An event name
• {string|Function} selector - A selector to match | An event listener
• {Function} [handler] - An event listener

const body = delegate(document.body);

body.on('click', '#button', () => {
  alert('Clicked!');
});

// If the base element itself handles the event:
body.on('click', () => {
  alert('Clicked');
});

one

Registers an event listener that is fired only once.

• {string} eventName - An event name
• {string|Function} selector - A selector to match | An event listener, which is fired only once.
• {Function} [handler] - An event listener, which is fired only once.

const container = delegate(document.querySelector('.container'));

container.one('click', '#button', () => {
  alert('Clicked!');
});

// If the base element itself handles the event:
container.one('click', () => {
  alert('Clicked');
});

off

Removes registered event listeners.

• {string} [eventName] - An event name. If omit it, all the listeners will be removed.
• {string|Function} [selector] - A selector to match | An event listener
• {Function} [handler] - An event listener. If omit it, all the listeners that are corresponded to the eventName will be removed.

const handler1 = () => alert('Clicked!');
const handler2 = () => alert('Clicked!');
const handler3 = () => alert('Mouse Over!');

delegate(document)
  .on('click', '#button', handler1)         // No.1
  .on('click', '#button', handler2)         // No.2
  .on('mouseover', '#button', handler3)     // No.3
  .on('click', handler1);                   // No.4

// To remove only event No.1:
delegate(document).off('click', '#button', handler1);

// To remove only event No.4:
delegate(document).off('click', handler1);

// To remove all click events registered to #button (No.1 and No.2):
delegate(document).off('click', '#button');

// To remove all click events (No.1, No.3 and No.4):
delegate(document).off('click');

// To remove all events:
delegate(document).off();

clear

Removes all registered event listeners. It is almost the same as off().

delegate(document).clear();

Event Object

Listeners receive an event object when an event is fired. This object provides the following methods and properties:

Methods

• preventDefault()
• stopPropagation()
• stopImmediatePropagation()

Properties

• originalEvent - a genuine event object when an event is fired
• currentTarget - the current element

delegate(document)
  .on('click', 'a', evt => {
      evt.preventDefault();
  })
  .on('mousedown', '#area', evt => {
      if (evt.originalEvent.pageX < 48 && evt.originalEvent.pageY < 48) {
        console.log('Shoot!');
      }
  })
  .on('blur', 'input[type="text"]', evt => {
      // evt.currentTarget === this
      console.log(evt.currentTarget.value);
  })

Passive Listener

You can specify a passive listener like this:

const listener = evt => {
  // Error (It cannot be prevent this event).
  evt.preventDefault();
};

delegate(document)
  .on('touchstart:passive', '.touch-area', listener);

Note that the touchstart:passive is clearly distinguished from touchstart. If you want to remove this listener, you need to write like this:

delegate(document)
  .off('touchstart:passive', '.touch-area', listener);

Method Chaining

This library supports method chaining like jQuery.

delegate(document)
  .on('mousedown', '#button', () => {
    alert('Mouse down!');
  })
  .on('mouseover', '#button', () => {
    alert('Mouse over!');
  })
  .on('mouseup', '#button', () => {
    alert('Mouse up!');
  });

Browser Support

Chrome, Firefox, Safari, Edge

License

MIT