[$rootScope:infdig] Infinite digest cycle detected

The error [$rootScope:infdig] Infinite digest cycle detected in AngularJS occurs when the AngularJS $digest cycle goes into an infinite loop. This happens when Angular’s change detection mechanism continuously re-evaluates the model because something in the application is causing the model to change repeatedly during the digest cycle.

In AngularJS, the $digest cycle is responsible for checking and updating the model and the view. If a model is updated during this cycle, AngularJS will re-run the $digest cycle to check for any changes again. If this happens repeatedly, it creates an infinite loop, which AngularJS detects and throws the [$rootScope:infdig] error to prevent the browser from hanging.

Step 1: Understanding the Digest Cycle

In AngularJS, the $digest cycle checks if any changes have occurred in the application’s data and updates the view accordingly. This process happens automatically when you update a model bound to the view.

When AngularJS runs the $digest cycle, it iterates over all watchers (variables that are being observed for changes), comparing their new values with their old ones. If any value changes, it triggers a re-evaluation of the digest cycle. This continues until no more changes are detected or the maximum number of iterations is reached.

An infinite digest cycle occurs if, during the cycle, Angular detects a change that causes the $digest cycle to run again without reaching a stable state.

Step 2: Common Causes of Infinite Digest Cycle

Here are some common reasons why this error occurs:

1. Model Changes Inside Watchers or $digest Cycle: If you are making changes to the model (i.e., updating variables) inside a $watch or any other part of the digest cycle, it can cause AngularJS to run the $digest cycle repeatedly.
2. Scope Variables Changing Continuously: If the value of a scope variable changes continuously during the $digest cycle, AngularJS will keep triggering the cycle until the maximum iteration count is reached, leading to an infinite loop.
3. Using $timeout or $interval Improperly: Sometimes, using $timeout or $interval to update variables inside a controller can inadvertently trigger an infinite digest cycle if not done carefully. For instance, if $timeout triggers a model change within the $digest cycle, this can create a loop.
4. Improper $scope.$apply() Usage: Calling $scope.$apply() manually while the digest cycle is already running will cause another $digest cycle to be initiated, which could lead to an infinite loop.
5. Recursive Digest Cycle Triggering: Recursive function calls that trigger model changes during their execution can cause AngularJS to re-enter the digest cycle. This is often caused by recursive watchers or event listeners.

Step 3: How to Fix the [$rootScope:infdig] Error

1. Avoid Changing the Model Inside a Watcher

When using $watch or any function that’s part of the digest cycle, avoid making changes to the model inside the watcher. If the model is modified inside the $digest cycle, it will cause AngularJS to re-run the cycle, which might result in an infinite loop.

Example of a problematic watcher:

$scope.$watch('someModel', function(newValue, oldValue) {
    // Changing the model inside the watcher triggers a new digest cycle
    $scope.someModel = 'New Value'; // This causes an infinite digest loop
});

Instead, try to perform the model change outside of the digest cycle or use $timeout to delay the change:

$scope.$watch('someModel', function(newValue, oldValue) {
    // Use $timeout to change the model outside the digest cycle
    $timeout(function() {
        $scope.someModel = 'New Value'; // This won't trigger an infinite loop
    });
});

2. Use $timeout to Update the Model Safely

If you need to update the model after some time or inside another cycle, wrap the changes inside $timeout. This ensures that the changes happen outside the current $digest cycle, preventing infinite loops.

Example:

$scope.someFunction = function() {
    // $timeout delays the update, preventing an infinite loop
    $timeout(function() {
        $scope.someModel = 'New Value';
    });
};

3. Avoid Recursive $scope.$apply() Calls

If you are calling $scope.$apply() manually, make sure it is not inside an already running digest cycle. If you call $scope.$apply() while AngularJS is in the middle of a digest cycle, it will trigger a new cycle and potentially cause an infinite loop.

Example of incorrect usage:

$scope.someFunction = function() {
    // This can cause an infinite digest cycle if it's inside an already running cycle
    $scope.someModel = 'New Value';
    $scope.$apply(); // This re-triggers a digest cycle inside an existing one
};

To avoid this, only call $scope.$apply() when necessary and outside of any ongoing $digest cycles. Angular will usually call $digest automatically in response to most model changes.

4. Check for Circular Dependencies in Watchers

Ensure that the watchers or model bindings do not have circular dependencies. Circular references in scope variables or functions can cause AngularJS to get stuck in a loop, trying to resolve them.

For example, if you have two models that depend on each other:

$scope.modelA = $scope.modelB;
$scope.modelB = $scope.modelA;  // This creates a circular dependency and an infinite loop

Instead, structure your data and logic to avoid circular dependencies. If you need to reference one model in another, consider using a service or computed property to break the cycle.

5. Use $evalAsync for Async Updates

If you need to perform an asynchronous update without triggering a full digest cycle, use $evalAsync. This queues the update to happen in the next digest cycle rather than immediately, helping avoid infinite loops caused by synchronously triggering updates.

Example:

$scope.someFunction = function() {
    $scope.$evalAsync(function() {
        $scope.someModel = 'Updated Value'; // This update is scheduled for the next digest cycle
    });
};

6. Debugging Infinite Loops

To debug infinite loops, start by isolating the part of your code where the $digest cycle is being triggered repeatedly. Use console.log() to inspect the values of scope variables and their changes during the digest cycle. You can also log the call stack to see where the loop is originating.

Example:

console.log('Digest Cycle Triggered');
console.log($scope.someModel);

7. Limit Digest Cycle Iterations

You can also modify the $rootScope settings to limit the maximum number of iterations in a digest cycle. Although this is not a recommended solution, it can help you avoid the infinite loop for debugging purposes. If you choose to do this, be aware that it’s better to fix the underlying issue.

$scope.$root.$$phase = null; // Reset the digest cycle manually (not recommended for production)

Step 4: Final Considerations

1. Be Mindful of $timeout and $interval: These functions can trigger updates to the scope, which can inadvertently trigger further digest cycles. Always ensure these functions are used correctly to avoid introducing infinite loops.
2. Structure Your Code to Avoid Recursive Updates: Recursive function calls or complex watchers can quickly escalate into infinite loops. Always try to refactor your logic to avoid recursive updates.
3. Use Angular Services for Complex Logic: If you are manipulating data or logic that involves multiple variables being updated in tandem, consider using Angular services to manage these updates more efficiently.