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+.

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

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

$ npm install --save mitt

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

// using ES6 modules
import mitt from 'mitt'

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

The UMD build is also available on unpkg:

<script src="https://unpkg.com/mitt/dist/mitt.umd.js"></script>

You can find the library on window.mitt.

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

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

import mitt from 'mitt';

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

const emitter = mitt<Events>(); // inferred as Emitter<Events>

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:

import mitt, { Emitter } from 'mitt';

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

const emitter: Emitter<Events> = mitt<Events>();

Preact + Mitt Codepen Demo

• mitt
• all
• on
  • Parameters
• off
  • Parameters
• emit
  • Parameters

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

Returns Mitt

A Map of event names to registered handler functions.

Register an event handler for the given type.

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

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

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

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

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

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

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

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.

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/<your-username>/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.

MIT License © Jason Miller