Is it possible to create a promise loop until reject in angular

Question

I wish to load ~10000 resources and doing this all at once during the resolve phase takes a bit too long due to certain calculations being done. So then I came to the idea to load the resources page by page sequentially, however since all these resources need to be visible (on a map) standard, user-input based pagination, doesn't really work.

I know that promises can be chained like:

promise.then(doThis).then(doThat).then(doWhat);

And I know that an array of promises can be resolved with $q.all like:

$q.all([doThis, doThat, doWhat]);

However what I want to is to call the same promise again and again in series until I hit a rejection.

Example:

function next() {
  var deferred = $q.defer();
  if(someCondition) {
    deferred.reject();
  } else {
    //do something
    //store data somewhere
    deferred.resolve();
  }

  return deferred.promise;
}

Let's say that this function does some $http calls and stores the result somewhere in the service/controller. If it hits a certain condition (perhaps there aren't any pages anymore or an http error) it rejects a promise, otherwise it resolves it.

Now I'd like to do something like this pseudocode

$q.loop(next).untilError(handleError);

Where next will be called in a loop upon resolving the previous next call, until rejection.

Is something like this possible?

Joy · Accepted Answer · 2015-08-24 11:21:12Z

2

Check the console of this demo: JSFiddle.

It ensures the calling of the APIs are using userId from 1 to 5 sequentially. And stop at some condition (userId > 5).

angular.module('Joy', [])
    .controller('JoyCtrl', ['$scope', '$http', function ($scope, $http) {

    getUser(1, getUser);

    function getUser(userId, next) {
        if (userId > 5) {
            console.log('Enough. Stop');
            return;
        }
        $http.get('http://jsonplaceholder.typicode.com/posts?userId=' + userId).then(function (data) {
            console.log(data.data);
            next(userId + 1, next);
        });
    }
}]);

edited Aug 24, 2015 at 11:21

answered Aug 24, 2015 at 10:55

Joy

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