At what point is the resolution of two-way binding for services injected into a controller typically completed?

I am puzzled by the behavior of the code snippet below, as it only produces the following output:

Array []
Array [object, object]

Instead, when submitting the form, I anticipate the output to be:

Array [object, object]
Array [object, object]

You can view the code here.

Why does the line

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

not immediately update the service?

Any insights would be greatly appreciated. Thank you.

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);
      };


    }]);

Answer №1

The updates for your service were not being received because you have replaced the reference of the service object postsFactory.posts_list that is stored in $scope.posts with a different array using the following code:

 $scope.posts = [
    {title: 'post 1', upvotes: 5},
  ];

As a result, any changes made to $scope.posts will not affect the object in the service since they now point to separate references. You can confirm this by trying the following:-

 $scope.posts.push({title: 'post 1', upvotes: 5});

If both properties maintain the same reference, any changes will be reflected on both sides.

Answer №2

  $scope.posts = postsFactory.posts_list;

When you set $scope.posts to equal postsFactory.posts_list, you are not creating a binding. Instead, you are simply assigning the reference value of postsFactory.posts_list to $scope.posts. This reference is then replaced with a new array in the following code:

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

As a result, $scope.posts now points to a completely different list, leaving the original postsFactory.posts_list orphaned and unaffected by any changes made in the addPost function.

To understand this better, I recommend looking into AngularJS watchers as they play a crucial role here.

Furthermore, for two-way databinding, it's common practice to use directives like ng-bind or {{bindme}} syntax in templates, especially for beginners.

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