Why is the $scope variable value not being updated in Angular JS controller?

Question

Why is the $scope variable value not being updated in Angular JS controller?

My controller code snippet is shown below. I am trying to access the value of $scope.FCGId. How can I access this variable?

 angular.module('hotelApp.controllers')
     .controller('menuCtrl', ['$scope','menu'
         function($scope,'menu') {

             $scope.categories = [];
             $scope.FCGId = 0

             $scope.items = [];

             $scope.getCategories = function() {
                 menu.getCategories().success(function(data) {
                     $scope.categories = data;
                     $scope.FCGId = data['rows'][0].GRPCOD;

                 });
             }

             $scope.getItems = function(gropuId) {
                 menu.getItems(gropuId).success(function(data) {
                     $scope.items = data;
                     console.log(data);
                 });
             }

             $scope.$on('$ionicView.afterEnter', function() {
                 $scope.getCategories();
                 console.log($scope.FCGId);
                 $scope.getItems($scope.FCGId);

             });
         }
     ]);

The code above is returning 0 instead of the updated value from the getCategories() function.

javascript angularjs

Answer 1

Answer №1

Alrighty

$scope.obtainCategories function initiates an asynchronous call during the event below

$scope.$on('$ionicView.afterEnter', function() {
                 $scope.obtainCategories();
                 console.log($scope.FCGId);
                 $scope.fetchItems($scope.FCGId);

             });

When $scope.obtainCategories() is invoked, it triggers an asynchronous request.

However, the script does not wait for this call to finish. It attempts to access the $scope.FCGId variable in console.log($scope.FCGId); without proper initialization due to the incomplete asynchronous call.

A solution for this issue would be:

Either calling $scope.obtainCategories function at the beginning of the controller as an initialization step, or returning a promise from the $scope.obtainCategories function, or utilizing a promise in an alternative manner based on your specific needs.

CODE MODIFICATION.

Define $scope.obtainCategories in the following manner

Inject $q into your controller.

var defer = $q.defer();       
$scope.obtainCategories = function() {
                 menu.loadCategories().success(function(data) {
                    $scope.categories = data;
                   // $scope.FCGId = data['rows'][0].GRPCOD;
                    defer.resolve(data['rows'][0].GRPCOD);  
                    return defer.promise;

                 });
             }

and handle the event like this

 $scope.$on('$ionicView.afterEnter', function() {
                 $scope.obtainCategories().then(function(successData){
                 $scope.FCGId = successData
                  console.log($scope.FCGId);
                 });

                 $scope.fetchItems($scope.FCGId);

             });

Alternative Solution -2. Since there are no dependencies in calling the $scope.obtainCategories function, it can be executed at the beginning of the controller.

The same approach can be applied to the call to $scope.fetchItems as well.

Answer 2

Alrighty

$scope.obtainCategories function initiates an asynchronous call during the event below

$scope.$on('$ionicView.afterEnter', function() {
                 $scope.obtainCategories();
                 console.log($scope.FCGId);
                 $scope.fetchItems($scope.FCGId);

             });

When $scope.obtainCategories() is invoked, it triggers an asynchronous request.

However, the script does not wait for this call to finish. It attempts to access the $scope.FCGId variable in console.log($scope.FCGId); without proper initialization due to the incomplete asynchronous call.

A solution for this issue would be:

Either calling $scope.obtainCategories function at the beginning of the controller as an initialization step, or returning a promise from the $scope.obtainCategories function, or utilizing a promise in an alternative manner based on your specific needs.

CODE MODIFICATION.

Define $scope.obtainCategories in the following manner

Inject $q into your controller.

var defer = $q.defer();       
$scope.obtainCategories = function() {
                 menu.loadCategories().success(function(data) {
                    $scope.categories = data;
                   // $scope.FCGId = data['rows'][0].GRPCOD;
                    defer.resolve(data['rows'][0].GRPCOD);  
                    return defer.promise;

                 });
             }

and handle the event like this

 $scope.$on('$ionicView.afterEnter', function() {
                 $scope.obtainCategories().then(function(successData){
                 $scope.FCGId = successData
                  console.log($scope.FCGId);
                 });

                 $scope.fetchItems($scope.FCGId);

             });

Alternative Solution -2. Since there are no dependencies in calling the $scope.obtainCategories function, it can be executed at the beginning of the controller.

The same approach can be applied to the call to $scope.fetchItems as well.

Answer 3

Answer №2

The issue you're facing is due to the fact that JavaScript typically runs faster than asynchronous calls return, causing your $scope.getItems function to execute before $scope.getCategories has completed.

To ensure the order of API calls, you can utilize a powerful concept known as promises. There are plenty of resources available on the topic, simply search for "angular promise" to learn more =)

Update: Another straightforward approach is to leverage the success function:

$scope.getCategories = function() {
    menu.getCategories().success(function(data) {
        $scope.categories = data;
        $scope.FCGId = data['rows'][0].GRPCOD;

        $scope.getItems($scope.FCGId);  // this line
    });
}

$scope.getItems = function(groupId) {
    menu.getItems(groupId).success(function(data) {
        $scope.items = data;
        console.log(data);
    });
}

$scope.$on('$ionicView.afterEnter', function() {
    $scope.getCategories();
    console.log($scope.FCGId);
    // $scope.getItems($scope.FCGId);  // remove this line
});

By following this method, you can avoid dealing with $q and other promise-related complexities.

Answer 4

The issue you're facing is due to the fact that JavaScript typically runs faster than asynchronous calls return, causing your $scope.getItems function to execute before $scope.getCategories has completed.

To ensure the order of API calls, you can utilize a powerful concept known as promises. There are plenty of resources available on the topic, simply search for "angular promise" to learn more =)

Update: Another straightforward approach is to leverage the success function:

$scope.getCategories = function() {
    menu.getCategories().success(function(data) {
        $scope.categories = data;
        $scope.FCGId = data['rows'][0].GRPCOD;

        $scope.getItems($scope.FCGId);  // this line
    });
}

$scope.getItems = function(groupId) {
    menu.getItems(groupId).success(function(data) {
        $scope.items = data;
        console.log(data);
    });
}

$scope.$on('$ionicView.afterEnter', function() {
    $scope.getCategories();
    console.log($scope.FCGId);
    // $scope.getItems($scope.FCGId);  // remove this line
});

By following this method, you can avoid dealing with $q and other promise-related complexities.

Answer 5

Answer №3

It appears that the menu.getCategories() function is running asynchronously, resulting in a delayed execution and causing the $scope.FCGId to be set as 0.

To address this issue, you can provide a callback function as the second parameter to the getCategories function. This callback function will handle the necessary assignments and subsequent calls.

$scope.setFCGValue = function(data) {
     $scope.categories = data;
     $scope.FCGId = data['rows'][0].GRPCOD;
     $scope.getItems($scope.FCGId);
};

$scope.$on('$ionicView.afterEnter', function() {
     menu.getCategories().success($scope.setFCGValue);
});

By passing a custom function as a callback, we ensure that the required operations are carried out after the completion of the getCategories() function.

Answer 6

It appears that the menu.getCategories() function is running asynchronously, resulting in a delayed execution and causing the $scope.FCGId to be set as 0.

To address this issue, you can provide a callback function as the second parameter to the getCategories function. This callback function will handle the necessary assignments and subsequent calls.

$scope.setFCGValue = function(data) {
     $scope.categories = data;
     $scope.FCGId = data['rows'][0].GRPCOD;
     $scope.getItems($scope.FCGId);
};

$scope.$on('$ionicView.afterEnter', function() {
     menu.getCategories().success($scope.setFCGValue);
});

By passing a custom function as a callback, we ensure that the required operations are carried out after the completion of the getCategories() function.

Why is the $scope variable value not being updated in Angular JS controller?

Answer №1

Answer №2

Answer №3

Similar questions

Utilizing dynamic variables in Angular Translate Rails: a tutorial

Maintain the structure of the slick slider during transitions

How come my links aren't initiating jQuery click events?

Creating a Cascading State and City Dropdown Using Knockout JS and JSON Data

What causes discrepancies between jQuery set attributes and .html() output?

Turn off the ability to view the content of .css and .js files within the browser

Is Next.js the Ultimate Serverless Rendering Tool with Cloudflare Workers?

A jquery class for styling with CSS

Gaining entry to a JSON object within an array

Using an id as the attribute value for a React ref

I am facing difficulties in showing the data in my Ionic view when attempting to connect to my php API

Providing static content within the generated code structure by Yeoman for the Angular Fullstack framework

Is there a way to choose all elements in the Bootstrap pagination code using JavaScript?

What is the proper way to bind CoreUI's CSwitch component?

JavaScript functions are not being triggered when the submit button is clicked

How to Build a Custom Toolbar with Left and Right Aligned Elements using React.js and Material UI

Display the personalized list of user items on the MERN dashboard

What is the best way to retrieve an ng-model parameter within a controller?

What is the process for exporting data from MongoDB?

Understanding the process of unmarshalling an array within a POST request