Is Promise.resolve a asynchronous function?

Question

When I have the following code:

var promise1 = Promise.resolve([1, 2, 3]);

promise1.then((value) => {
  console.log(value);
  // expected output: Array [1, 2, 3]
});


console.log('end of script');

I know that end of script is returned earlier because the promise is asynchronous. But at what point of execution does it become asynchronous?

Is Promise.resolve() asynchronous? Or is .then asynchronous or even both functions? Is there some other mechanism playing under the hood?

(was a hell to google because I get only results of the new async await features)

Answer 1

 Promise.resolve([1, 2, 3]);

Is Promise.resolve() asynchronous?

No that's just a regular function call. It will return a result immediately.

Or is .then asynchronous or even both functions

No. Both aren't asynchronous in the sense that

promise1.then((value) => console.log(value));

will immediately return a new Promise for chaining.

However a Promise definitely resolves asynchronously, which means that the inner function (value => console.log(value)) is called definitely after your whole synchronous code executed.

Is there some other mechanism playing under the hood?

Yes there is a "magic" event loop in the background which manages all the async events.