How to execute code, while promise is resolving

Question

Assuming I have a function foo() which returns a promise. How would I "start" the async function foo(), execute some code while foo() is resolving, and then go on with the rest of the code after foo() resolved?

// start async function foo
const somePromise = foo(); // do not use await here in order to execute the following lines
// synchronous code
const a = ....;
const b = ....;
// and then, go on with the rest of the code after the synchronous (const a = ..., const b = ...) and asynchronous (foo()) parts have finished
if(somePromise resolved) { // how to check for resolved promise here
    // go on
    const bar = a + b;
}

Answer 1

Pretty funny you even use the word then in your question, but:

const somePromise = foo();
// do something synchronous while foo() is resolving
// and then, go on with the rest of the code after the synchronous and asynchronous parts have finished

somePromise.then(() => {
  // go on
});

You're better off handling this immediately;

foo().then(() => {
  // go on
});

// This happens synchronously

Variant of the first, with await:

const somePromise = foo();
// do something synchronous while foo() is resolving
// and then, go on with the rest of the code after the synchronous and asynchronous parts have finished

await somePromise;
// go on