Mittt

Tiny functional event emitter / pubsub. Forked from https://github.com/developit/mitt New project created from TSDX CLI.

• Microscopic: weighs ~300 bytes gzipped size
• Useful: a wildcard "*" event type listens to all events
• Useful: a wildcard "*" emit invokes all registered handlers
• Useful: a wildcard "*!" emit invokes all unique registered handlers
• Functional: methods don't rely on this

Mittt was made for the browser, but works in any JavaScript runtime. It has no dependencies and supports IE11+.

Table of Contents

• Install
• Usage
• Smallest-Install

Install

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

npm install mittt
# or
# yarn add mittt

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

// using ES6 modules
import mittt from 'mittt'

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

The ESM build is also available on unpkg:

<script type="module" src="https://unpkg.com/mittt/dist/mittt.esm.js"></script>

Usage

import mittt from 'mittt'

const emitter = mittt()

function onEvent(eventType, payload) {
  console.log(eventType, payload)
}

// Listen to an event
emitter.on('foo', onEvent)

// Listen to all events
emitter.on('*', onEvent)

// Fire an event
emitter.emit('foo')

// Fire an event with payload
const payload = { a: 'b' }
emitter.emit('bar', payload)

// Fire all registered handlers with payload
emitter.emit('*', payload) // payload is optional

// Given these listeners. Both onEvent would be invoked on '*' emit.
emitter.on('foo', onEvent)
emitter.on('bar', onEvent)
emitter.emit('*', payload)

// Fire all unique registered handlers with payload
emitter.emit('*!', payload) // payload is optional

// Given these listeners. Only one onEvent would be invoked on '*!' emit.
emitter.on('foo', onEvent)
emitter.on('bar', onEvent)
emitter.emit('*!', payload)

// Given these listeners. Both handlers would be invoked on '*!' emit.
emitter.on('foo', (eventType, payload) => {})
emitter.on('bar', (eventType, payload) => {})
emitter.emit('*!', payload)

// Working with handler references:
emitter.on('foo', onEvent) // listen
emitter.off('foo', onEvent) // unlisten

// Initiate emitter with on event setup
const eventHandlerMap = Object.create(null)
eventHandlerMap.foo = [
    (eventType, payload) => {
      console.log(eventType, payload) // foo, 123
    },
    (eventType, payload) => {
      console.log(eventType, payload) // foo, 123
    },
  ]
const emitter = mittt(eventHandlerMap)

emitter.emit('foo', 123) // all handlers for foo are invoked

TypeScript

import mittt, { Emitter, EventHandler } from 'mittt'
const emitter: Emitter = mittt()

let foo: EventHandler = (eventType, payload) => {}

emitter.on('foo', foo)

Smallest-Install

If you want to install the smallest size without wildcard (*) support. ~200 bytes gzipped size.

npm install mittt@^1
# or
# yarn add mittt@^1