use $http inside custom provider in app config, angular.js

Question

The main question - is it possible? I tried with no luck..

main app.js

...
var app = angular.module('myApp', ['services']);
app.config(['customProvider', function (customProvider) {

}]);
...

provider itself

var services = angular.module('services', []);
services.provider('custom', function ($http) {
});

And I've got such error:

Uncaught Error: Unknown provider: $http from services 

Any ideas?

Thanks!

Answer 1

The bottom line is:

• You CANNOT inject a service into the provider configuration section.
• You CAN inject a service into the section which initializes the provider's service.

Details:

Angular framework has a 2 phase initialization process:

PHASE 1: Config

During the config phase all of the providers are initialized and all of the config sections are executed. The config sections may contain code which configures the provider objects and therefore they can be injected with provider objects. However, since the providers are the factories for the service objects and at this stage the providers are not fully initialized/configured -> you cannot ask the provider to create a service for you at this stage -> at the configuration stage you cannot use/inject services. When this phase is completed all of the providers are ready (no more provider configuration can be done after the configuration phase is completed).

PHASE 2: Run

During run phase all the run sections are executed. At this stage the providers are ready and can create services -> during run phase you can use/inject services.

Examples:

1. Injecting the $http service to the provider initialization function WILL NOT work

//ERRONEOUS
angular.module('myModule').provider('myProvider', function($http) {
    // SECTION 1: code to initialize/configure the PROVIDER goes here (executed during `config` phase)
    ...

    this.$get = function() {
        // code to initialize/configure the SERVICE goes here (executed during `run` stage)

        return myService;
    };
});

Since we are trying to inject the $http service into a function which is executed during the config phase we will get an error:

Uncaught Error: Unknown provider: $http from services 

What this error is actually saying is that the $httpProvider which is used to create the $http service is not ready yet (since we are still in the config phase).

2. Injecting the $http service to the service initialization function WILL work:

//OK
angular.module('myModule').provider('myProvider', function() {
    // SECTION 1: code to initialize/configure the PROVIDER goes here (executed during `config` phase)
    ...

    this.$get = function($http) {
        // code to initialize/configure the SERVICE goes here (executed during `run` stage)

        return myService;
    };
});

Since we are now injecting the service into the service initialization function, which is executed during run phase this code will work.

Answer 2

This might give you a little leverage:

var initInjector = angular.injector(['ng']);
var $http = initInjector.get('$http');

But be careful, the success/error callbacks might keep you in a race-condition between the app start and the server response.