Angularjs, wait for a nested promise

Question

I have 3 services that return 3 promises, but the third needs the data from the second, so I call it inside the second. I want to wait for all the three promises to be solved, this is the way that I implemented, but doesn't work (waits only for the first and the second).

var promise1, promise2, promise3;

promise1 = service1();
promise2 = service2();

promise2.then(function (data) {
  promise3= service3(data);

});

$q.all([ promise1, promise2, promise3]).then(function success() {
 //somehing
});

Mizzen

Answer 1

You can assign the second promise's then() callback with a returned promise from the third service.

var promise1, promise2, promise3;

promise1 = service1();
promise2 = service2();

promise3 = promise2.then(function (data) {
  return service3(data);
});

$q.all([ promise1, promise2, promise3]).then(function success() {
 //somehing
});

Encaustic

Ok, so maybe I miss something. Isn't $q.all already satisfied when I enter in promise2.then? – Mizzen

No, since it waits for promise3 to get resolved. It is mentioned in the AngularJS $q documentation that the .then() function will return a new promise. – Encaustic

@ryeballarhow to test it? imagine it's Jasmine & Angular test. Could you please update your answer? – Engler

I'd just like to add that in my situation, where I had even further nested promises, I found some success by adding the nested promises to the existing promise array variable used by the first $q.all() and adding a second $q.all() in the .then() of the first. (Followed by another .then() with the stuff I wanted to wait to do!) This waited again with the new promises. You could repeat this for further layers, but perhaps already we're in the territory of bad design. – Kiln

Answer 2

Have you tried to nest your promise 2 inside promise 1, and then put your final resolve inside the promise 3 delegate?

That's pretty slick code and I'm certainly no expert, but have had to wait to accomplish things on other service calls and have had to do things like that.

Hasan