Mitt

> Tiny 200b functional event emitter / pubsub.

- Microscopic: weighs less than 200 bytes gzipped
- Useful: a wildcard "*" event type listens to all events
- Familiar: same names & ideas as Node's EventEmitter
- Functional: methods don't rely on this
- Great Name: somehow mitt wasn't taken

Mitt was made for the browser, but works in any JavaScript runtime. It has no dependencies and supports IE9+.

Table of Contents

- Install
- Usage
- Examples & Demos
- API
- Contribute
- License

Install

This project uses node and npm. Go check them out if you don't have them locally installed.

``sh
$ npm install --save mitt
`

Then with a module bundler like rollup or webpack, use as you would anything else:

`javascript
// using ES6 modules
import mitt from 'mitt'

// using CommonJS modules
var mitt = require('mitt')
`

The UMD build is also available on unpkg:

`html

`

You can find the library on window.mitt.

Usage

`js
import mitt from 'mitt'

const emitter = mitt()

// listen to an event
emitter.on('foo', e => console.log('foo', e) )

// listen to all events
emitter.on('*', (type, e) => console.log(type, e) )

// fire an event
emitter.emit('foo', { a: 'b' })

// clearing all events
emitter.all.clear()

// working with handler references:
function onFoo() {}
emitter.on('foo', onFoo) // listen
emitter.off('foo', onFoo) // unlisten
`

$3

Set "strict": true in your tsconfig.json to get improved type inference for mitt instance methods.

`ts
import mitt from 'mitt';

type Events = {
foo: string;
bar?: number;
};

const emitter = mitt(); // inferred as Emitter

emitter.on('foo', (e) => {}); // 'e' has inferred type 'string'

emitter.emit('foo', 42); // Error: Argument of type 'number' is not assignable to parameter of type 'string'. (2345)
`

Alternatively, you can use the provided Emitter type:

`ts
import mitt, { Emitter } from 'mitt';

type Events = {
foo: string;
bar?: number;
};

const emitter: Emitter = mitt();
`

Examples & Demos


Preact + Mitt Codepen Demo





*

API

#### Table of Contents

- mitt
- all
- on
- Parameters
- off
- Parameters
- emit
- Parameters

$3

Mitt: Tiny (~200b) functional event emitter / pubsub.

Returns Mitt

$3

A Map of event names to registered handler functions.

$3

Register an event handler for the given type.

#### Parameters

- type (string \| symbol) Type of event to listen for, or '*' for all events
- handler Function Function to call in response to given event

$3

Remove an event handler for the given type.
If handler is omitted, all handlers of the given type are removed.

#### Parameters

- type (string \| symbol) Type of event to unregister handler from, or '*'
- handler Function? Handler function to remove

$3

Invoke all handlers for the given type.
If present, '*' handlers are invoked after type-matched handlers.

Note: Manually firing '\*' handlers is not supported.

#### Parameters

- type (string \| symbol) The event type to invoke
- evt Any? Any value (object is recommended and powerful), passed to each handler

Contribute

First off, thanks for taking the time to contribute!
Now, take a moment to be sure your contributions make sense to everyone else.

$3

Found a problem? Want a new feature? First of all see if your issue or idea has already been reported.
If don't, just open a new clear and descriptive issue.

$3

Pull requests are the greatest contributions, so be sure they are focused in scope, and do avoid unrelated commits.

- Fork it!
- Clone your fork: git clone https://github.com//mitt
- Navigate to the newly cloned directory: cd mitt
- Create a new branch for the new feature: git checkout -b my-new-feature
- Install the tools necessary for development: npm install
- Make your changes.
- Commit your changes: git commit -am 'Add some feature'
- Push to the branch: git push origin my-new-feature`
- Submit a pull request with full remarks documenting your changes.

License

MIT License © Jason Miller