mapLimit without callback only executes "limit" amount of times

What version of async are you using? 3.1.0

Which environment did the issue occur in (Node version/browser version) node: 10.16.0

What did you do? Please include a minimal reproducible case illustrating issue.

"use strict";
const delay = (timeout) => {
    return new Promise((resolve) => {
        setTimeout(resolve, timeout);
    });
};
const myAsyncFunction = async function () {
    return async.mapLimit([1, 2, 3, 4, 5], 3, async (num) => {
        await delay(2000);
        console.log(num * 2);
        return num * 2;
    });
};
myAsyncFunction().then((result) => {
    console.log(result);
});

https://codepen.io/bertyhell/pen/NWKMRvY?editors=0012

What did you expect to happen? The code should output: 2, 4, 6, 8, 10 Then at the end of the mapLimit the code should log the array: [2, 4, 6, 8, 10]

What was the actual result? The code outputs: 2, 4, 6 The final then is never called, the await on the async.mapLimit just hangs

[bertyhell]

Yes, then it works: tsconfig.json:

{
  "compilerOptions": {
    "target": "es2017"
  }
}

This means async v3 isn’t compatible with typescript for targets < es2017 😭

I thought you detected an async function because no callback method is passed.

Or would that cause breaking changes for people that didn’t pass a callback, but still expected the callback version of the async lib function to be used?

[aearly]

If typescript is compiling async functions down to generator function, then Async can’t tell if it’s an async function or a callback-accepting function. Can you tell TS to target ES2017 rather than ES2015?

The other (ugly) solution is to wrap async functions with asyncify:

    return async.mapLimit([1, 2, 3, 4, 5], 3, asyncify(async (num) => {
        await delay(2000);
        console.log(num * 2);
        return num * 2;
    }));