AngularJS: Prevent error $digest already in progress when calling $scope.$apply()

This article will show how you can prevent the error $digest already in progress when calling $scope.$apply() in AngularJS.

AngularJS provides powerful tools for managing data binding and updating the view. However, sometimes when working with asynchronous operations or integrating with external APIs, you may encounter the error $digest already in progress. This error occurs when you attempt to call $scope.$apply() or $scope.$digest() while AngularJS is already in the process of digesting the scope.

Understanding the Problem

AngularJS uses a digest cycle to keep the view in sync with the model. If you try to initiate another digest cycle while one is already in progress, it can lead to this error. Developers often attempt to use $scope.$apply() or $scope.$digest() with conditional checks like if(!$scope.$$phase), but this is not a recommended practice.

Now, have a look at the methods below to prevent this error and ensure smooth integration of asynchronous operations with AngularJS.

Using $timeout

One common approach to prevent the $digest already in progress error is by using AngularJS’s built-in $timeout service. The $timeout service executes a callback function after a specified delay, and AngularJS automatically triggers a $scope.$apply() after the callback execution, ensuring that the changes are properly propagated to the view.

$timeout(function() {
  // Any code in here will automatically have an $scope.apply() run afterwards
  $scope.myVariable = newValue;
});

By using $timeout, you can safely update the scope within asynchronous operations without worrying about the timing of the digest cycle.

Using _.defer() (with lodash or underscore)

If you are using lodash or underscore in your AngularJS project, you can also utilize the _.defer() function to achieve the same result. Similar to $timeout, _.defer() delays the execution of a function until the current call stack has cleared, ensuring that the changes are applied within the AngularJS context.

_.defer(function() {
  $scope.$apply();
});

Using _.defer() provides an alternative approach for triggering $scope.$apply() after asynchronous operations.

Best Practices and Considerations

This section provides additional guidance and considerations for developers. It covers points such as avoiding the use of $$phase directly, evaluating performance implications of the chosen approach, and introducing the $evalAsync() method as an alternative for uncertain code execution timing.

Avoid Using $$phase

Accessing $$phase directly is discouraged as it is a private property of the framework. Instead, rely on official AngularJS services and functions to manage the digest cycle.

Consider Performance Implications

While using $timeout or _.defer() effectively prevents the $digest already in progress error, be mindful of the performance implications, especially in scenarios where frequent updates to the scope are required. Evaluate the necessity of triggering a digest cycle and optimize your code accordingly.

Use $evalAsync

Since AngularJS 1.2, the $evalAsync() method has been introduced as a powerful alternative for executing code within the current digest cycle or initiating a new one if none is in progress. Consider using $evalAsync() in scenarios where the timing of code execution is uncertain, such as asynchronous callbacks.

Example

$scope.$evalAsync(function() {
    // Your code here will be executed in the current or next digest cycle.
    $scope.myVar = newValue;
});

In the above code, the $scope.$evalAsync ensures that the code within the provided function is executed within the AngularJS digest cycle.

This is particularly useful when making changes to the model asynchronously, preventing common errors related to the “$digest already in progress” issue.

Conclusion

Here, we’ve explored various strategies for preventing the $digest already in progress error in AngularJS applications. By leveraging $timeout, _.defer(), or $evalAsync(), you can safely update the scope within asynchronous operations without encountering digest cycle conflicts. Remember to adhere to best practices and consider the performance implications of each approach in your AngularJS project.