Return value of Promise's resolve/reject functions

Question

Consider this situation.

new Promise(function(resolve, reject) {
    var x = resolve(2);
});

What value will x be? I tried to print it and it showed me undefined. It is intuitive, but is it always so? Is it in docs?

Second question

new Promise(function(resolve, reject) {
    resolve(2);
    return 5;
});

What should we return from the function that we put into a promise? Is this value ignored?

Benjamin Gruenbaum · Accepted Answer · 2015-07-27T11:24:50.057

7

The return value of the promise constructor is ignored.

The resolve function also returns undefined.

This was first specified in the promise constructor spec and later in the ES2015 (ES6) language specification.

edited Jul 27 '15 at 11:24

answered Jul 27 '15 at 11:19

@MichałKownacki I've added citations, namely check the note in http://www.ecma-international.org/ecma-262/6.0/index.html#sec-promise-executor – Benjamin Gruenbaum Jul 27 '15 at 11:26
Yeah but I'm using node.js with Bluebird, it uses Promises/A+ standard. – Michał Kownacki Jul 27 '15 at 12:07
@MichałKownacki not only does bluebird behave this way, in 3.0 we warn against it: http://imgur.com/a/t3xng – Benjamin Gruenbaum Jul 27 '15 at 12:08

1 Answers1