Nice to have in ES2017 async/await development
const asyncjs = require('async');
const foo = async () => {
const arr = Array.from({ length: 1000 }, (v, i) => i);
const transformedArr = await asyncjs.mapLimit(arr, 100, async (v) => {
return await Promise.resolve(v * 2);
});
console.log(transformedArr);
}
Historically, async
has been against this (see #1086).
However, with the new async/await
syntax, node adding promise APIs in the future, and the support for promises having increased, I'd be open to revisiting this. Thoughts @aearly @megawac?
I've thought about this, and experimented with it a bit. People are going to want to await Async.mapLimit(arr, 10, async foo => {...})
. It could very well be something we include in 3.0.
Also, some Async methods would be pretty silly with async/await, e.g. series
, waterfall
.
When using Async I sort of naturally assumed the return of a Promise. It was only at the dis-functioning of my code and my routine rtfm moment that I noticed the callback structure. The above would be very welcome since it would keep code as uniform ES7 as possible.
I agree that this would be useful.
In the interim, if anyone is stuck right now, I found this article good for explaining how to write a forEach loop with await.
https://codeburst.io/javascript-async-await-with-foreach-b6ba62bbf404
Finally dug out my old experiment: #1526
+1
function makeAsync() {
if (arguments.length < 3) return; // wrong params, not run or throw exception here!
let fixParams = {};
let paramLength = arguments.length;
let method = arguments[0];
for (let i = 1; i < arguments.length; i++) {
fixParams[(i - 1)] = arguments[i];
}
return new Promise((resolve, reject) => {
const callback = (err, result) => {
if (err) return reject(err);
return resolve(result);
};
fixParams[paramLength - 1] = callback;
fixParams.length = paramLength;
method.apply(null, fixParams);
});
}
example1:
await makeAsync(async.each, openFiles, async (file) => {
await asyncOperation(file);
});
example2:
const foo = async () => {
const arr = Array.from({ length: 1000 }, (v, i) => i);
const transformedArr = await makeAsync(async.mapLimit, arr, 100, async (v) => {
return await Promise.resolve(v * 2);
});
console.log(transformedArr);
}
@tritoanst, your promisify function is overhead. It may be easier:
function promisify(original) {
return function (...args) {
return new Promise((resolve, reject) => {
args.push((err, result) => {
if (err) {
reject(err);
} else {
resolve(result);
}
});
original.apply(this, args);
});
};
}
const foo = async () => {
const arr = Array.from({ length: 1000 }, (v, i) => i);
const transformedArr = await promisify(async.mapLimit)(arr, 100, async (v) => {
return v * 2; // `return await` is redundant
});
console.log(transformedArr);
};
Most helpful comment
I've thought about this, and experimented with it a bit. People are going to want to
await Async.mapLimit(arr, 10, async foo => {...})
. It could very well be something we include in 3.0.Also, some Async methods would be pretty silly with async/await, e.g.
series
,waterfall
.