function promiseCompletionSource() {
	let resolve;
	let reject;

	const promise = new Promise((res, rej) => {
		resolve = res;
		reject = rej;
	});

	return {
		promise: promise,
		resolve: resolve,
		reject: reject
	};
}

// ...

var b = promiseCompletionSource();
b.promise.then(x => console.log(x));
b.resolve(123);