Using angular. injector with ngAnimate

I have included "ngAnimate" as a dependency on my ngApp.

Now in the jQuery file I am trying to access it using:

angular.injector(['ng', 'angular-sm']).invoke(['$compile', '$timeout' ,function ($compile, $timeout) {

      

        
        
        
      

    

But it gives me an error

Error: $injector:unpr
Unknown Provider
Unknown provider: $rootElementProvider <- $rootElement <- $animate <- $compile

      

        
        
        
      

    

And then I changed this to:

angular.injector(['ng','ngAnimate', 'angular-sm']).invoke(['$compile', '$timeout' ,function ($compile, $timeout) {

angular.injector(['ng','ngAnimate', 'angular-sm']).invoke(['$animate','$compile', '$timeout' ,function ($animate,$compile, $timeout) {

      

        
        
        
      

    

And they are NOT USED.

Then I tried:

var app_element = document.querySelector('[ng-app=angular-sm]');
            angular.element(app_element).injector().invoke(['$compile', '$timeout' ,function($compile,$timeout) {

      

        
        
        
      

    

I took the ngApp injector and it worked. Why is that?