Injecting $state (ui-router) into $http interceptor causes circular dependency

The question is a duplicate of AngularJS: Injecting service into a HTTP interceptor (Circular dependency)

I am re-posting my answer from that thread here:

A Better Fix

I think using the $injector directly is an antipattern.

A way to break the circular dependency is to use an event: Instead of injecting $state, inject $rootScope. Instead of redirecting directly, do

this.$rootScope.$emit("unauthorized");

plus

angular
    .module('foo')
    .run(function($rootScope, $state) {
        $rootScope.$on('unauthorized', () => {
            $state.transitionTo('login');
        });
    });

That way you have separated the concerns:

1. Detect a 401 response
2. Redirect to login

Jonathan's solution was great until I tried to save the current state. In ui-router v0.2.10 the current state does not seem to be populated on initial page load in the interceptor.

Anyway, I solved it by using the $stateChangeError event instead. The $stateChangeError event gives you both to and from states, as well as the error. It's pretty nifty.

$rootScope.$on('$stateChangeError',
    function(event, toState, toParams, fromState, fromParams, error){
        console.log('stateChangeError');
        console.log(toState, toParams, fromState, fromParams, error);

        if(error.status == 401){
            console.log("401 detected. Redirecting...");

            authService.deniedState = toState.name;
            $state.go("login");
        }
    });

The Fix

Use the $injector service to get a reference to the $state service.

var interceptor = ['$location', '$q', '$injector', function($location, $q, $injector) {
    function success(response) {
        return response;
    }

    function error(response) {

        if(response.status === 401) {
            $injector.get('$state').transitionTo('public.login');
            return $q.reject(response);
        }
        else {
            return $q.reject(response);
        }
    }

    return function(promise) {
        return promise.then(success, error);
    }
}];

$httpProvider.responseInterceptors.push(interceptor);

The Cause

angular-ui-router injects the $http service as a dependency into $TemplateFactory which then creates a circular reference to $http within the $httpProvider itself upon dispatching the interceptor.

The same circular dependency exception would be thrown if you attempt to inject the $http service directly into an interceptor like so.

var interceptor = ['$location', '$q', '$http', function($location, $q, $http) {

Separation of Concerns

Circular dependency exceptions can indicate that there is a mixing of concerns within your application which could cause stability issues. If you find yourself with this exception you should take the time to look at your architecture to ensure you avoid any dependencies that end up referencing themselves.

@Stephen Friedrich's answer

I agree with the answer below that using the $injector to directly get a reference to the desired service is not ideal and could be considered an anti pattern.

Emitting an event is a much more elegant and also decoupled solution.