How to use $q's constructor syntax with Angular $http's config.timeout?

Question

Since Promise is now officially spec-ed and all, how do I convert the $q.defer() promise creation in the following snippet to use the $q(function (resolve, reject) {}) constructor syntax instead?

// Cancel any ongoing $http request so that only the most recent $http
// callback gets invoked
var canceller;
function getThing(id) {
  if (canceller) canceller.resolve();
  canceller = $q.defer();

  return $http.get('/api/things/' + id, {
    timeout: canceller.promise
  });
}

(Fyi from $http docs: timeout is "… in milliseconds, or promise that should abort the request when resolved.")

I don't get what your goal is. Your code is fine and working, there's no reason to change anything. — Bergi
– Bergi, Commented Mar 23, 2016 at 0:09
"How do I use the promise constructor syntax?" - You don't! — Bergi
– Bergi, Commented Mar 23, 2016 at 0:09
Note that the native Promise object does not have a "deferred" api. It seems like timeout should be able to accept any then-able object here. — thatmarvin
– thatmarvin, Commented Mar 23, 2016 at 14:45
Oh wait, now I get it. You don't want to convert the $http.get call, but the $q.defer creation to use the Promise constructor? — Bergi
– Bergi, Commented Mar 23, 2016 at 14:46

Bergi · Accepted Answer · 2016-03-23 14:49:00Z

1

I'd do it like this:

var canceller = null;
function getThing(id) {
  if (canceller) canceller();
  return Promise.resolve($http.get('/api/things/' + id, {
    timeout: new Promise(function(resolve) {
      canceller = resolve;
    })
  }));
}

I'll assume you'd never have used canceller.reject anyway, so you can just keep around the resolve function itself to call it next time.

answered Mar 23, 2016 at 14:49

Bergi

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3 Comments

thatmarvin Over a year ago

$http.get() returns a promise, so I don't think it needs the Promise.resolve() wrap?

Bergi Over a year ago

@thatmarvin: It doesn't return one of those shiny new officially specced Promises, but an old boring AngularJs-promise :-) If you want to use Angular promises (and $q instead of new Promise) then you can omit it of course.

thatmarvin Over a year ago

gotcha, accepted. very obvious now that i see it, thanks!

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