arguments.callee not returning a callable function when async

Question

I have been playing around with arguments.callee and stumbled upon this problem.

My idea was that the anonymous function would run on startup and then again after a few seconds.

 setTimeout(async function() { console.log('Not working') return arguments.callee }(), 1000) 

I have no issues if my anonymous function isn't async

 setTimeout(function() { console.log('Working just fine') return arguments.callee }(), 1000) 

The thing has me baffled is that, when I console.log(arguments.callee) in the async function, it comes up just fine.

 setTimeout(function() { console.log(arguments.callee) }, 1000) setTimeout(async function() { console.log(arguments.callee) }, 2000) 

Can anyone explain to me why it doesn't work when the function is async ?

Answer 1

This is because when you return something from an async function it is wrapped in a Promise , so the arguments.callee is actually the function you want to return but it is wrapped inside a promise.

From MDN :

An asynchronous function is a function which operates asynchronously via the event loop, using an implicit Promise to return its result.

 (async function() { console.log('Not working') return arguments.callee }()).then((fun) => fun()); //the wrapped function can be executed in the chained then callback 

As @ Oliver Nybo pointed out in the comment, we can also use await inside an async context to wait for the promise to be resolved with the function value:

 (async () => { setTimeout(await async function() { console.log('Not working'); return arguments.callee; }(), 1000) })();