streetstrider / emitter

event emitter

emitter

single- and multi-channel event emitter

Features

• Single-channel emitter — no event name, just a list of subscriptions.
• Multi-channel emitter (like EventEmitter or nanoevents).
• Minimal overhead.
• Fast, optimized emit.
• Minimal memory footprint, proper garbage collection.
• Provides disposer.
• Fully tested & 100% coverage.
• TypeScript defs.
• TypeScript defs are fully tested.
• utility: once.
• utility: when.
• Emitter is 557 characters when minified (952 for Multi).

API / Example

import Emitter from '@streetstrider/emitter'
import once from '@streetstrider/emitter/once'

const emitter = Emitter()

const disposer = emitter.on((a, b) => console.log(a + b))
const disposer = once(emitter, (a, b) => console.log(a + b))

emitter.emit(1, 2)

disposer()

emitter.is_empty() // → true

import MultiEmitter from '@streetstrider/emitter/multi'
import { multi as once_multi } from '@streetstrider/emitter/once'

const emitter = MultiEmitter()

const ds1 = emitter.on('plus', (a, b) => console.log(a + b))
const ds2 = emitter.on('mul',  (a, b) => console.log(a * b))

const ds3 = once_multi(emitter, 'plus', (a, b) => console.log(a + b))
const ds4 = once_multi(emitter, 'mul',  (a, b) => console.log(a * b))

emitter.emit('plus', 1, 2)
emitter.emit('mul', 3, 4)

ds1()
ds2()

emitter.is_empty() // → true

import Emitter from '@streetstrider/emitter'
import when from '@streetstrider/emitter/when'

const emitter = Emitter()

async function do_async () {
  const next_one = await when(emitter) /* would capture first emission */
}

emitter.emit('next_one')
emitter.emit('next_two')
emitter.emit('next_three')

Types

Built-in TypeScript type definitions.

const emitter = Emitter<[number, number]>()
const emitter = MultiEmitter<{ plus: [number, number] }>()

Some design solutions

Why are once and when not in the core?

Because they are not part of the minimal API. Making them public methods on emitter would also make them non-tree-shakeable and the only gain would be consistent syntax with on (via dot). If you still want this, you can patch your emitters by binding/partialing (bring your own) once and/or when. You can also attach them by currying them.

import once from '@streetstrider/emitter/once'

const emitter = Emitter()

emitter.once = once.bind(null, emitter)
emitter.once = partial(once, emitter)

const disposer = emitter.once((a, b) => console.log(a + b))

import { multi as once_multi } from '@streetstrider/emitter/once'

const emitter = MultiEmitter()

emitter.once = once_multi.bind(null, emitter)
emitter.once = partial(once_multi, emitter)

const disposer = emitter.once('plus', (a, b) => console.log(a + b))

License

ISC, © Strider, 2023.