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I am trying to figure out promises... What is the difference between simply making an $http request, then acting upon whether is what successful (.success()) & it failing (.fail()), in comparison to a promise (q = $q.defer()) with q.resolve()?

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  • I'm not sure I understand your question. How are you making a $http request with $q.defer? If you don't make a request, then that's obviously the difference. Commented Jul 2, 2015 at 19:57

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$http itself uses $q. These both services are not operating at the same level.

$http.get(url) returns a promise that can be resolved or rejected. It means that you are using a promise delivered by a service ($http). Internally, $http will call $q.defer(), then $q.resolve() or $q.reject(). This will call either your .success() or .fail() method.

$q is a service to create your own promise.

Using $q is a great way to learn about promises but in your case, $http is already doing that work for you.

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The $http legacy promise methods success and error/fail have been deprecated. docs.angularjs.org/api/ng/service/$http#deprecation-notice
Yes, success and error/fail have been deprecated in favor of then. But the core answer stays the same. $http returns a promise and $q "creates" a promise. Within then() you still have two callback functions for success and fail. $http
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Nothing. $http methods return promises. In short, they can also be chained with then. success and fail are sugar for resolve-only and reject-only thens.

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