Is there a way in AngularJS to define constants with other constants?

Question

I'm trying to define constants with other constants, but it seems that it can't be done, because the initial constant isn't ready when the required constant depending require it. I want to be sure if this isn't possible at all.

Currently I have constants in this way:

angular.module('mainApp.config', [])     .constant('RESOURCE_USERS_DOMAIN', 'http://127.0.0.1:8008')     .constant('RESOURCE_USERS_API', 'http://127.0.0.1:8008/users')     // Specific routes for API     .constant('API_BASIC_INFORMATION', RESOURCE_USERS_API + '/api/info')     .constant('API_SOCIAL_NETWORKS', RESOURCE_USERS_API + '/api/social')     ; 

The second two constants are what I want to accomplish.

Answer 1

The AngularJS way to define dependencies between Controllers, Services and others is by dependency injection (DI). So if you have a controller A that depends on a service B you would have to create it like this:

var myApp = angular.module("exampleApp",[]);  myApp.controller("aCtrl", function(serviceB){     // Controller functionally here }); 

See, AngularJS will check the serviceB dependency and look for the service you created with that name. If you don't create one you will get an error.

So, if you want to create a constant A that depends on constant B, you would need to tell angular that A depends on B. But a constant can't have a dependency. A constant can return a function, but the DI won't work for the constant. Check this Fiddle so you can see for which methods DI work for.

So answering your question, you can't define a constant with other constants.

But you can do this:

angular.module('projectApp', [])   .constant('domain', 'http://somedomain.com')   .constant('api', '/some/api/info')   .service('urls', function(domain, api) {this.apiUrl = domain + api;})    .controller('mainCtrl',function($scope,urls) {        $scope.url = urls.apiUrl;    }); 

Check this fiddle to see it working:

If you want to understand more about DI, check out this post.

Answer 2

An easy way to do this is like this:

var myApp = angular.module("exampleApp",[]);  myApp.constant('RESOURCES', (function() {   // Define your variable   var resource = 'http://127.0.0.1:8008';   // Use the variable in your constants   return {     USERS_DOMAIN: resource,     USERS_API: resource + '/users',     BASIC_INFO: resource + '/api/info'   } })()); 

And use the constants like this:

myApp.controller("ExampleCtrl", function(RESOURCES){   $scope.domain = RESOURCES.USERS_DOMAIN; }); 

Credits: link