Javascript: Return a promise inside async function

Question

Would it make any difference if I have:

async function test () {
  const foo = await bar()
  return Promise.all([promise1, promise2])
}

instead of:

async function test () {
  const foo = await bar()
  const [result1, result2] = await Promise.all([promise1, promise2])
  // Given that I don't care about result1, result2 in this `test` function
  return [result1, result2]
}

I get the same result if I do either. E.g. I can do this for either case:

test().then(([result1, result2]) => { ... })

but I am more curious about the underlying mechanism how they both behave the same.

In other words, how does async function handle it if inside the function I return a promise instead of a value?

Answer 1

I think you're effectively calling synchronous-like functions with await within the promise chain which, according to this answer:

You are perfectly free to call either synchronous functions within the promise chain (from within .then() handlers) or asynchronous functions that then return a new promise.

When you return something from a .then() handler, you can return either a value (which becomes the resolved value of the parent promise) or you can return another promise (which chains onto the previous promise) or you can throw which works like returning a rejected promise (the promise chain becomes rejected).