Async: how to make async work with async/await

Created on 14 Feb 2019 · 10Comments · Source: caolan/async

var async = require('async');

var workPool = async.queue(async (task, taskComplete)=>{
  console.log(1, taskComplete);

  async.retry(3, async (retryComplete)=>{

    console.log(2, retryComplete);
    // retryComplete(null, task);

  });
});

workPool.push("test");

I wonder why i got this result:

$ node test.js
1 undefined
2 undefined

question

Source

kazaff

Most helpful comment

@pawelotto I think for that you can use node promisify util, I didn't test but since the main callback function signature is compatible I assume it will work.

So the example above will become (without handling error):

import async from "async"
import {promisify} from "util"

const promiseMapLimit = promisify(async.mapLimit)
const results = await promiseMapLimit(files, async file => { // <- no callback!
    const text = await util.promisify(fs.readFile)(dir + file, 'utf8')
    const body = JSON.parse(text) // <- a parse error herre will be caught automatically
    if (!(await checkValidity(body))) {
        throw new Error(`${file} has invalid contents`) // <- this error will also be caught
    }
    return body // <- return a value!
})

b4dnewz on 13 May 2019

👍2

All 10 comments

https://caolan.github.io/async/

Async accepts async functions wherever we accept a Node-style callback function. However, we do not pass them a callback, and instead use the return value and handle any promise rejections or errors thrown.
async.mapLimit(files, async file => { // <- no callback!
    const text = await util.promisify(fs.readFile)(dir + file, 'utf8')
    const body = JSON.parse(text) // <- a parse error herre will be caught automatically
    if (!(await checkValidity(body))) {
        throw new Error(`${file} has invalid contents`) // <- this error will also be caught
    }
    return body // <- return a value!
}, (err, contents) => {
    if (err) throw err
    console.log(contents)
})

ex1st on 14 Feb 2019

Yep, Async doesn't pass callbacks to async functions -- just return when the task is complete.

aearly on 14 Feb 2019

And what about returning values from the final callback function (instead of console-log them like in this example)?

pawelotto on 11 Mar 2019

Just return ing values from async functions works in most cases.

aearly on 11 Mar 2019

Which async function exactly returns a value? From what I've checked they return void, e.g.
doUntil

pawelotto on 11 Mar 2019

@pawelotto I think for that you can use node promisify util, I didn't test but since the main callback function signature is compatible I assume it will work.

So the example above will become (without handling error):

import async from "async"
import {promisify} from "util"

const promiseMapLimit = promisify(async.mapLimit)
const results = await promiseMapLimit(files, async file => { // <- no callback!
    const text = await util.promisify(fs.readFile)(dir + file, 'utf8')
    const body = JSON.parse(text) // <- a parse error herre will be caught automatically
    if (!(await checkValidity(body))) {
        throw new Error(`${file} has invalid contents`) // <- this error will also be caught
    }
    return body // <- return a value!
})

b4dnewz on 13 May 2019

👍2

Maybe you can try neo-async

kazaff on 15 May 2019

❤1

@kazaff cool, I didn't know about it, thanks!

b4dnewz on 15 May 2019

@kazaff Legend!

pawelotto on 15 May 2019

@kazaff how to use neo-async in b4dnewz's answer, just fail to return reulst