@uxuip/emitter

Simple event emitter/pubsub library.

• Only 300~ bytes (minified).
• The on method returns unbind function. You don’t need to save callback to variable for removeListener.
• TypeScript and ES modules support.
• Implementation using Map and Set

import { createEmitter } from '@uxuip/emitter'

const emitter = createEmitter()
const result = []

const unbind = emitter.on('tick', (value1, value2) => {
  result.push(value1 + value2)
})

emitter.emit('tick', 2, 4)
unbind()
emitter.emit('tick', 2, 4)

console.log(result) // [6]

• Install
• TypeScript
• Add Listener
• Remove Listener
• Execute Listeners
• Events List
• Once
• Remove All Listeners

Install

npm install @uxuip/emitter

TypeScript

accepts interface with event name to listener argument types mapping.

import { createEmitter, EventsMap } from '@uxuip/emitter'

interface Events extends EventsMap {
  set: [name: string, count: number]
  plus: [number, number]
  push: [...number[]]
  call: []
}
// or
// type Events = {}

const emitter = createEmitter<Events>()

// Correct calls:
emitter.emit('set', 'prop', 1)
emitter.emit('plus', 2, 2)
emitter.emit('push', 1, 2, 3, 4)
emitter.emit('call')

// Compilation errors:
emitter.emit('set', 'prop', '1')
emitter.emit('plus', '2', 2)
emitter.emit('push', '1', 2, 3, 4)
emitter.emit('call', '1')

Add Listener

Use on method to add listener for specific event:

emitter.on('tick', (number) => {
  console.log(number)
})

emitter.emit('tick', 1)
// Prints 1
emitter.emit('tick', 5)
// Prints 5

Remove Listener

Methods on returns unbind function. Call it and this listener will be removed from event.

const unbind = emitter.on('tick', (number) => {
  console.log(`on ${number}`)
})

emitter.emit('tick', 1)
// Prints "on 1"

unbind()
emitter.emit('tick', 2)
// Prints nothing

Execute Listeners

Method emit will execute all listeners. First argument is event name, others will be passed to listeners.

emitter.on('tick', (a, b) => {
  console.log(a, b)
})
emitter.emit('tick', 1, 'one')
// Prints 1, 'one'

Events List

You can get used events list by events property.

const unbind = emitter.on('tick', () => { })
console.log(emitter.listens)
// Map

Once

If you need add event listener only for first event dispatch, you can use this snippet:

const unbind = emitter.on('tick', (...args) => {
  unbind()
  console.log(...args)
})
emitter.emit('tick', 1, 2)
// 1 2

Remove All Listeners

emitter.on('event1', () => {})
emitter.on('event2', () => {})

emitter.listens.clear()