ASW (async & await)

A library to help developer use async functions as promises.

install

npm i asw

Usage

ES6:

import {
  asyncx,
  awaitx,
  asyncEach,
  asyncMap,
  asyncFind
  asyncSeries,
  asyncParallel,
  asyncIterate,
} from 'asw'

CommonJS:

const {
  asyncx,
  awaitx,
  asyncEach,
  asyncMap,
  asyncFind
  asyncSeries,
  asyncParallel,
  asyncIterate,
} = require('asw')

In browser:

<script src="node_modules/asw/dist/asw.js"></script>
<script>
const {
  asyncx,
  awaitx,
  asyncEach,
  asyncMap,
  asyncFind
  asyncSeries,
  asyncParallel,
  asyncIterate,
} = window['asw']
</script>

Notice: native Promise should be supported.

API

asyncx(fn, native?)

Convert a function to be async function, no matter it is a normal function or an async function.

// normal function:
let fn = (arg1) => { ... }
let afn = asyncx(fn)

// async function:
let fn = async (arg1) => { ... }
let afn = asyncx(fn)

It is useful when you do not know whether a function is an aysnc function or not in runtime.

function async calc(fn) {
  let v = await asyncx(fn)() // here I do not know whether `fn` is an async function or not
  return v
}

native

default: false

For ES default behaviour, async function will run synchronously before reach first await syntax, for example:

async function get(url) {
  console.log(1)
  await fetch(url)
  console.log(2)
}
get('...')
console.log(3)

// => 1
// => 3
// => 2

As default, asyncx converts a function to be a completely synchronous function. If you want to use native behaviour, you can set native to be true:

const get = asyncx(function(url) {
  console.log(1)
  awaitx(fetch(url), () => console.log(2))
}, true) // notice here
get('...')
console.log(3)

// => 1
// => 3
// => 2

awaitx(input, yield)

Convert a normal value or a promise to be a promise.

let x = 3
let a = awaitx(x) // a is a promise which resolve with `x`
let b = awaitx(a, a => a + 12) // b is a promise which resolve with `x + 12`

b.then(b => console.log(b)) // 16

Here, a and b are promises which resovle fn return value.

• input: a normal value or a promise instance
• yield: a function which use input to calculate, can be a normal function or an async function
• @return: a promise defer which resolved whith yield return value

Use asyncx and awaitx to write async function like:

const get = asyncx(function(url) {
  let res = awaitx(fetch(url))
  let data = awaitx(res, res => res.json())
  return data
})

/*
async function get(url) {
  let res = await fetch(url)
  let data = await res.json()
  return data
}
*/

get('http://xxx').then(data => { ... })

Here get function is defined very like an async function. However, the syntax of await is much more easy than awaitx, here we have to use a function to calculate the value.

// usage1: with a normal value
let defer = awaitx('xxx')

// usage2: with a promise
let defer = awaitx(Promise.resolve('xxx'))

// usage3: with a normal value and a normal function
let defer = awaitx('xxx', x => x + 'xx')

// usage4: with a promise and normal function
let defer = awaitx(Promise.resolve('xxx'), x => x + 'xx')

// usage5: with a normal value and an async function
let defer = awaitx(url, async url => await fetch(url))

As you see, the first parameter can be a normal value or a promise, the second parameter can be a normal function or an async function. If the first parameter is a promise, its resolve value will be used as the second paramater function's parameter. The second parameter should be a function, its return value will be used as awaitx return value. If the second parameter is an async function, the resolve value will be used as awaitx return value.

asyncEach(items, fn)

Traverse items with async function one by one.

let items = [...]
await asyncEach(items, async (item, i, arr) => {
  // ...
})

asyncFor(start, end, step, fn)

Iterate from start to stop by step.

await asyncForm(0, 10, 1, async (i, next, stop, complete) => {
  ...
})

asyncMap(items, fn)

Traverse items with async function and return an new array in a promise.

let items = [...]
let newItems = await asyncEach(items, async (item, i) => {
  // ...
  return item
})

New items will be returned when all async function finish. In a forEach loop, fn will run in parallel.

asyncFind(items, fn)

Traverse items with async function and return the find item.

const items = [...]
const item = await asyncFind(items, async (item, i) => {
  if (i === 2) {
    return true
  }
  return false
})

asyncIterate(items, fn)

Iterate items with async function.

const items = []
await asyncIterate(items, async (item, i, next, stop, complete) => {
  // ...
  setTimeout(next, 1000)
})

next

Iterate to next item.

stop

Stop (reject) iterating. The left iterator functions will not run any more.

Notice: next() or stop() should be called anyway! If you do not pass next, it will be treated as a resolved promise.

await asyncI(items, (item, i) => {
  console.log(item, i)
})

complete

Finish iterating by resolve a value.

const items = []
const found = await asyncIterate(items, async (item, i, next, stop, complete) => {
  if (item.type === 'animal') {
    complete(item)
  }
  else {
    next()
  }
})

We use previous code to find a item from an array.

asyncSeries(fns, ...args)

Calculate with args by async functions in serial.

let fns = [
  async (arg1, arg2) => { ... },
  async (arg1, arg2) => { ... },
]
await asyncSeries(fns, xx1, xx2)

Async functions will run with ...args one by one after each resolved, if one rejected, the letf ones will not run any more.

asyncParallel(fns, ...args)

Calculate with args by async functions in parallel.

let fns = [
  async (arg1, arg2) => { ... },
  async (arg1, arg2) => { ... },
]
await asyncParallel(fns, xx1, xx2)

Async functions will start with ...args at the same time, if one rejected, anthors will still run.