inside-out-async

Promises and async iterators are awesome, lets turn them inside out

Usage no npm install needed!

<script type="module">
  import insideOutAsync from 'https://cdn.skypack.dev/inside-out-async';
</script>

README

Inside Out Async

Release

It's pretty handy for turning things that are not promises and generators into promises and generators. Good for testing, but also for having more control over how things execute.

npm install inside-out-async

I nerd sniped myself and made this library. defer() is easily written in any new project, deferGenerator() is not.

Exports two functions

API

defer

function defer<T>(): Deferred<T>

interface Deferred<T> {
    promise: Promise<T>
    resolve: (value: T) => void
    reject: (error: Error) => void
}

Creates a promise and control functions. The promise is resolved and rejected by the control functions. Like the Promise constructor but inside out.

import { defer } from 'inside-out-async'
import { Trainer } from 'pokemon-trainer'

const pokemonCaught = defer()
const ash = new Trainer()
ash.on('capture', pokemonCaught.resolve)
ash.on('error', pokemonCaught.reject)

const pokemon = await pokemonCaught.promise
console.log(pokemon) // { name: 'Pikachu', temperament: 'surprised' }

deferGenerator

function deferGenerator<T, TReturn, TNext = unknown>(): DeferredGenerator<T, TReturn, TNext>

interface DeferredGenerator<T, TReturn, TNext> {
    generator: AsyncGenerator<T, TReturn, TNext>
    queueValue: (value: T) => void
    error: (err?: any) => void
    queueError: (err?: any) => void
    return: (value?: TReturn) => void
    queueReturn: (value?: TReturn) => void
}

Creates an async generator and control functions. The async generator yields values, errors, and returns based on the control functions.

  • queueValue queues a value to yielded next
  • error drops all queued values, puts the generator in a "done" state, and has the current pending or next call to next() throw an error
  • queueError puts the generator in a "done" state, and has the current pending or next call to next() throw an error
  • return() drops all queued values, and puts the generator in a "done" state with the passed in value
  • queueReturn() puts the generator in a "done" state with the passed in value
import { deferGenerator } from 'inside-out-async'

const pokedex = deferGenerator()
pokedex.queueValue({ name: 'Pikachu' })
pokedex.queueValue({ name: 'Bulbasaur' })
pokedex.queueValue({ name: 'Charizard' })
pokedex.queueReturn()

for await (const pokemon of pokedex.generator) {
  console.log(pokemon) // { name: 'Pikachu' }, { name: 'Bulbasaur' }, { name: 'Charizard' }
}