Discussion on: Limit concurrent asynchronous calls

[Benjamin Black]

As written, asyncLimit will not resolve until the async function completes, because of await p.catch(() => {});.

Instead,

const p = fn.apply(this, args);
pendingPromises.push(p);
p.finally(() => {
    pendingPromises = pendingPromises.filter(pending => pending !== p);
});
return p;

[YCM Jason]

But we need the async function fn to complete before resolving the async function (...args) {. Isn't it?

[Benjamin Black]

It's difficult to mentally follow the chain of promises here, because you have an async function (const asyncLimit = async...) which returns an async function (return async function) which itself awaits at least two promises (one in a loop) before resolving.

Note that asyncLimit does not have to be async, as it does not use await; removing async from the function signature would help comprehension a bit, since you would reduce one level of Promise-ception and stay out of limbo.

I guess it doesn't really matter, because the promise returned by asyncLimit can be used by the calling code. But attaching a finally clause to p instead of awaiting it allows the function to return immediately, instead of waiting for p to resolve.

[YCM Jason]

oh, I mistyped haha! Thanks for catching this!

asyncLimit shouldn't be an async function.