Run AngularJS initialization logic before main AngularJS app

bootstrapper.js

// define the module of the bootstrap app
var bootstrapModule = angular.module('bootstrapModule', []);

// the bootstrap service loads the config and bootstraps the specified app
bootstrapModule.factory('bootstrapper', function ($q, $http) {
    return {
        bootstrap: function (appName) {
            var deferred = $q.defer();

            // do initial loading here
            // in our case, this means doing any pre-init async http requests
            $q.all([$http.get('resources/test-a.json'), $http.get('/test-b.json')])
                .then(function (results) {
                    // when they're all loaded, start expanding our actual application
                    var app = angular.module(appName);

                    // declare app factories/constants/etc. that required pre-init here
                    // in our case, using a constant is the least invasive method to retain
                    // current functionality.
                    app.constant('TestAResponse', results[0]);
                    app.constant('TestBResponse', results[1]);

                    // we can now bootstrap the actual application.
                    angular.bootstrap(document, [appName]);
                    deferred.resolve();
            });

            return deferred.promise;
        }
    };
});

// Create a div which is used as the root of the bootstrap app
// in the run() function you can now use the bootstrapper service
// and shutdown the bootstrapping app after initialization of the actual app
var appContainer = document.createElement('div');
bootstrapModule.run(function (bootstrapper) {
    bootstrapper.bootstrap('app').then(function () {
        // removing the container will destroy the bootstrap app
        try {
            appContainer.remove();
        } catch (e) {

        }
    });
});

// make sure the DOM is fully loaded before bootstrapping
angular.element(document).ready(function () {
    angular.bootstrap(appContainer, ['bootstrapModule']);
});