"You must pass a resolver function as the first argument to the promise constructor"

Why is this a thing?

I have researched this a little bit and I can’t seem to find out why this is necessary at all. Can someone explain why you need to pass a function to the Promise constructor?

Is there some reason we cannot create a Promise or Deferred object that we will manually resolve at a later point?

For example, in jQuery, you can do the following, and it is extremely useful in multiple scenarios:

var deferred = new $.Deferred(); //works in jquery to give you a deferred object you can control manually

var deferred = new Promise(); //fails in the es6 Promise polyfill with the subject of this issue as an error msg.

Can we not perform a simple check on the Promise constructor, and return an object with a resolve and reject function if no function was passed? Why the need to wrap our functions in the promise constructor?

[petkaantonov]

Deferred is trivial to implement on top of the constructor:

function Deferred() {
    var d = {};
    d.promise = new Promise(function(resolve, reject) {
        d.resolve = resolve;
        d.reject = reject;
    });
    return d;
}

[SgtPooki]

+1 @petkaantonov exactly, thank you. I completely forgot about this… my bad.