bind-event-listener

A utility to make binding and (especially) unbinding DOM events easier. I seem to write this again with every new project, so I made it a library

import { bind, UnbindFn } from 'bind-event-listener';

const unbind: UnbindFn = bind(button, {
  type: 'click',
  listener: function onClick(event) {},
});

// when you are all done:
unbind();

import { bindAll } from 'bind-event-listener';

const unbind = bindAll(button, [
  {
    type: 'click',
    listener: function onClick(event) {},
    options: { capture: true },
  },
  {
    type: 'mouseover',
    listener: function onMouseOver(event) {},
  },
]);

// when you are all done:
unbind();

Rationale

When using addEventListener(), correctly unbinding events with removeEventListener() can be tricky.

1. You need to remember to call removeEventListener (it can be easy to forget!)

Example

target.addEventListener('click', onClick, options);

target.removeEventListener('click', onClick, options);

2. You need to pass in the same listener reference to removeEventListener

Example

target.addEventListener(
  'click',
  function onClick() {
    console.log('clicked');
  },
  options,
);

// Even those the functions look the same, they don't have the same reference.
// The original onClick is not unbound!
target.removeEventListener(
  'click',
  function onClick() {
    console.log('clicked');
  },
  options,
);

// Inline arrow functions can never be unbound because you have lost the reference!
target.addEventListener('click', () => console.log('i will never unbind'), options);
target.removeEventListener('click', () => console.log('i will never unbind'), options);

3. You need to pass in the same capture value option

Example

// add a listener: AddEventListenerOptions format
target.addEventListener('click', onClick, { capture: true });

// not unbound: no capture value
target.removeEventListener('click', onClick);

// not unbound: different capture value
target.removeEventListener('click', onClick, { capture: false });

// successfully unbound: same capture value
target.removeEventListener('click', onClick, { capture: true });
// this would also unbind (different notation)
target.removeEventListener('click', onClick, true /* shorthand for { capture: true } */);

// add a listener: boolean capture format
target.addEventListener('click', onClick, true /* shorthand for { capture: true } */);

// not unbound: no capture value
target.addEventListener('click', onClick);
// not unbound: different capture value
target.addEventListener('click', onClick, false);

// successfully unbound: same capture value
target.addEventListener('click', onClick, true);
// this would also unbind (different notation)
target.addEventListener('click', onClick, { capture: true });

bind-event-listener solves these problems

1. When you bind an event (or events with bindAll) you get back a simple unbind function
2. The unbind function ensures the same listener reference is passed to removeEventListener
3. The unbind function ensures that whatever capture value is used with addEventListener is used with removeEventListener

You will find an even fuller rationale for this project in my course: "The Ultimate Guide for Understanding DOM Events"

Usage

bind: basic

import { bind, UnbindFn } from 'bind-event-listener';

const unbind: UnbindFn = bind(button, {
  type: 'click',
  listener: onClick,
});

// when your are all done:
unbind();

bind: with options

import { bind } from 'bind-event-listener';

const unbind = bind(button, {
  type: 'click',
  listener: onClick,
  options: { capture: true, passive: false },
});

// when you are all done:
unbind();

bindAll: basic

import { bindAll } from 'bind-event-listener';

const unbind = bindAll(button, [
  {
    type: 'click',
    listener: onClick,
  },
]);

// when you are all done:
unbind();

bindAll: with options

import { bindAll } from 'bind-event-listener';

const unbind = bindAll(button, [
  {
    type: 'click',
    listener: onClick,
    options: { passive: true },
  },
  // default options that are applied to all bindings
  { capture: false },
]);

// when you are all done:
unbind();

When using defaultOptions for bindAll, the defaultOptions are merged with the options on each binding. Options on the individual bindings will take precedent. You can think of it like this:

const merged: AddEventListenerOptions = {
  ...defaultOptions,
  ...options,
};

Note: it is a little bit more complicated than just object spreading as the library will also behave correctly when passing in a boolean capture argument. An options value can be a boolean { options: true } which is shorthand for { options: {capture: true } }

Types

Thanks to the great work by @Ayub-Begimkulov bind-event-listener has fantastic TypeScript types

⚠️ TypeScript 4.1+ is required

import invariant from 'tiny-invariant';
import { bind } from 'bind-event-listener';

bind(window, {
  type: 'click',
  function: function onClick(event) {
    // `event` is correctly typed as a 'MouseEvent'
    // `this` is correctly typed as `window` (the event target that the event listener is added to)
  },
});

const button = document.querySelector('button');
invariant(button instanceof HTMLElement);

bind(button, {
  type: 'click',
  function: function onClick(event) {
    // `event` is correctly typed as a 'MouseEvent'
    // `this` is correctly typed as `button` (the event target that the event listener is added to)
  },
});

const object = {
  handleEvent: function onClick(event) {
    // `event` is correctly typed as a 'MouseEvent'
    // `this` is correctly typed as `object` (the event listener object that the event listener is added to)
  },
};

bind(button, {
  type: 'click',
  function: object,
});

Recipe: react effect

You can return a cleanup function from useEffect (or useLayoutEffect). bind-event-listener makes this super convenient because you can just return the unbind function from your effect.

import React, { useState, useEffect } from 'react';
import { bind } from 'bind-event-listener';

export default function App() {
  const [clickCount, onClick] = useState(0);

  useEffect(() => {
    const unbind = bind(window, {
      type: 'click',
      listener: () => onClick((value) => value + 1),
    });

    return unbind;
  }, []);

  return <div>Window clicks: {clickCount}</div>;
}

You can play with this example on codesandbox

Types

function bind(target: EventTarget, binding: Binding): UnbindFn;

function bindAll(
  target: EventTarget,
  bindings: Binding[],
  // AddEventListenerOptions is a built in TypeScript type
  sharedOptions?: boolean | AddEventListenerOptions,
): UnbindFn;

type Binding = {
  type: string;
  // EventListenerOrEventListenerObject is a built in TypeScript type
  listener: EventListenerOrEventListenerObject;
  options?: boolean | AddEventListenerOptions;
};

type UnbindFn = () => void;

Typescript built in DOM types: raw view, pretty view (warning: pretty view seems to crash Github!)

Cheers 👋

Brought to you by @alexandereardon