AngularJS dependency-injection

Question

I have say two modules:

1. foo.a
2. foo.b

and an application module:

  angular.module("foo", ["foo.a","foo.b"])

I have a service in module foo.b say:

  angular.module("foo.b", [])

  angular.module("foo.b").factory("helper",helperFn);

which I want to use in one of my controllers in foo.a.

What I have done is simple dependency injection:

 angular.module("foo.a", []);

 angular.module("foo.a")
        .controller("MyController",["helper",MyControllerFn]);

which is working.

My questions are

1. How am I getting the "helper" service from module foo.b even though it is not declared as a dependency for module a?
2. Will it break at a later stage?
3. If it is correct, is this a good practice?

Answer 1

Put the factory that you need access to in both modules in a third module. Have your two original modules inject a dependency to the third module.

angular.module("foo", ["foo.a", "foo.b"]);

angular.module("foo.a", ["foo.c"])
  .controller("MyController", ["helper", MyControllerFn]);

angular.module("foo.b", ["foo.c"]);

angular.module("foo.c")
  .factory("helper", helperFn);