$http propagate errors in promises

Question

so in this plnkr I demonstrate a failing $http request.

The responsibility of the service is to deconstruct the server response and to ready the information for the controller to consume.

When it errors, I feel like I need to propagate the error to the controller not for handling but for being able to inform the user that the operation couldn't complete. (handling in a sense of logging etc.)

As it stands:

return $http.get('notgoing')
  .then(
    function success(result) {
      return result.data;
    },
    function error(err) {
      console.warn(err); // do something meaningful with the error

      return err;
    }
  );

this will rollup the error or success into the chained promise's success function. This isn't ideal for informing the user.

Is there a simple way to get the error function to bubble the value as an error to the next chained promise's error function. (bearing in mind I don't really want to take a dependency on the $q library and have another promise interwoven with the $http promise)

- OR -

Does the responsibility of handling that error stop at the service.

Just a little addon: This [SO answer](http://stackoverflow.com/a/28703407/2375913) explains the difference between using `throw` and `reject`. — muenchdo, Sep 29 '15 at 13:14

Daniel A. White · Accepted Answer · 2015-09-29T13:05:07.630

3

Instead of return err;, throw it with throw err;. $q will handle the "uncaught" error and reject the chain.

edited Sep 29 '15 at 13:05

answered Sep 29 '15 at 13:01

Daniel A. White

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Genius.... I thought that throw would cause the entire app to bomb out. But fair enough! – Callum Linington Sep 29 '15 at 13:02
can you provide some explanation or just another link :) – Shreyas Sep 29 '15 at 13:02
@Shreyas to be fair if you take that throw and stick it into the plnkr there is enough explanation? – Callum Linington Sep 29 '15 at 13:03
thanks but I want to know the difference it would make while calling, as per my understanding it will call the error part of .then insted of success? – Shreyas Sep 29 '15 at 13:11

score 0 · Answer 2 · answered Sep 29 '15 at 13:03

0

I don't think there is a way without using $q, but Angular brings its own implementation along, so all you need to do is to inject it into your service and then call $q.reject(err). Otherwise Angular will think your error has already been handled inside the service.

angular.module('test', []).factory('testService', function ($http, $q) {
  ...  
  function test() {
    return $http.get('notgoing').then(function success(result) {
      return result.data;
    }, function error(err) {
      console.warn(err);
      return $q.reject(err);
    });
  }
});

Check the updated Plunker.

answered Sep 29 '15 at 13:03

muenchdo

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I did say I wanted to avoid this pattern. I do know of this. – Callum Linington Sep 29 '15 at 13:06
I know, but I thought there was no other way (which is incorrect). May I ask why you wish to avoid `$q`? – muenchdo Sep 29 '15 at 13:07

$http propagate errors in promises

2 Answers2