@ombro/mitten

Mitten is a lightweight event emitter library for TypeScript that allows you to create, manage, and emit custom events.

Installation

Use your favorite package manager to install it:

npm install @ombro/mitten
# or
pnpm add @ombro/mitten

Usage

Creating an Emitter

To create an emitter, you can use the mitten function. It takes an optional EventHandlerMap object as an argument, which is a map of event types and their corresponding event object.

import mitten from '@ombro/mitten'

type MyEvents = {
  foo: string
  bar: number
}

const emitter = mitten<MyEvents>()

Registering Event Handlers

To register an event handler, use the on method of the emitter. It takes two arguments: the event type to listen for, and the callback function to execute in response to the event.

emitter.on('foo', (event) => {
  console.log(`Received event with value: ${event}`)
})

To register a wildcard event handler that will execute for all events, use the on method with a '*' type and a callback that takes two arguments: the event type and the event object.

emitter.on('*', (type, event) => {
  console.log(`Received ${type} event with value: ${event}`)
})

Emitting Events

To emit an event, use the emit method of the emitter. It takes two arguments: the event type to emit, and the event object to pass to the event handlers.

emitter.emit('foo', 'hello world')

If you need to emit an event with an undefined value, pass undefined as the second argument to emit. You can also omit the second argument entirely if the event type has an optional value.

type MyEvents = {
  foo: string
  bar?: number
}

emitter.emit('foo', 'hello world')
emitter.emit('bar')

Unregistering Event Handlers

To unregister an event handler, use the off method of the emitter. It takes two arguments: the event type to unregister the handler from, and the optional callback function to remove.

const handler = (event: string) => {
  console.log(`Received event with value: ${event}`)
}

emitter.on('foo', handler)

// Unregister a specific handler
emitter.off('foo', handler)

// Unregister all handlers for a specific event type
emitter.off('foo')

// Unregister all handlers for wildcard event types
emitter.off('*')

Example

import mitten from '@ombro/mitten'

type MyEvents = {
  foo: string
  bar?: number
}

const emitter = mitten<MyEvents>()

emitter.on('foo', (event) => {
  console.log(`Received foo event with value: ${event}`)
})

emitter.on('bar', (event) => {
  console.log(`Received bar event with value: ${event}`)
})

emitter.on('*', (type, event) => {
  console.log(`Received ${type} event with value: ${event}`)
})

emitter.emit('foo', 'hello world')
emitter.emit('bar', 42)
emitter.emit('bar')