Angular Service Question

app.js

angular.module('flapperNews', [])
  .factory('postsFactory', [function(){
  	// Modularize posts frontend storage for better mock testing and independency of scope
    var posts_factory_object = {
        posts_list: []
    };
    return posts_factory_object;
  }])
  .controller('MainCtrl', [
  	'$scope',
  	'postsFactory',
  	function($scope, postsFactory){

      // Bind scope.posts to postsFactory.posts_list
      $scope.posts = postsFactory.posts_list;

  	  // Variable pseudo post data for test
  	  $scope.posts = [
        {title: 'post 1', upvotes: 5},
      ];

      // Frontend function for keeping track of state purely in frontend
      $scope.addPost = function(){
      	// Check if inputted string is undefinied or empty
      	if (!$scope.title || $scope.title ===''){ return; }

        $scope.posts.push({
        	title: $scope.title,
        	link: $scope.link, 
        	upvotes: 0
        });
        $scope.title = '';
        $scope.link = '';

        console.log(postsFactory.posts_list);
        console.log($scope.posts);
      };


  	}]);

index.html

        <form ng-submit="addPost()"
          style="margin-top:30px;">
          <h3>Add a new post</h3>
          <div class="form-group">
            <!--Store text input into title variable in MainCtrl scope-->
            <input type="text" 
              class="form-control"
              placeholder="Title" 
              ng-model="title"></input>
          </div>
          <div class="form-group">
            <!--Store text into $scope.link-->
            <input type="text" 
              class="form-control"
              placeholder="Link" 
              ng-model="link"></input>
          </div>
          <button type="submit">Post</button>
        </form>