angular.js/docs/content/error/rootScope/inprog.ngdoc

@ngdoc error
@name $rootScope:inprog
@fullName Action Already In Progress
@description

At any point in time there can be only one `$digest` or $apply operation in progress.
The stack trace of this error allows you to trace the origin of the currently executing $apply or $digest call.

`$digest` or `$apply` are processing operational states of the Scope - data-structure in Angular that provides context for models and enables model mutation observation.

Trying to reenter a `$digest` or `$apply` while one of them is already in progress is typically a sign of programming error that needs to be fixed.

This error is often seen when interacting with an API that is sometimes sync and sometimes async.

For example:

```
function MyController() {
  thirdPartyComponent.getData(function(someData) {
    scope.$apply(function() {
      scope.someData = someData;
    });
  });
}
```

The controller constructor is always instantiated from within an $apply cycle, so if the third-party component called our callback synchronously, we'd be trying to enter the $apply again.

To resolve this type of issue, either fix the api to be always synchronous or asynchronous or wrap the call to the api with setTimeout call to make it always asynchronous.


Other situation that leads to this error is when you are trying to reuse a function to by using it as a callback for code that is called by various apis inside and outside of $apply.

For example:

```
myApp.directive('myDirective', function() {
  return {
    link: function($scope, $element) {
      function doSomeWork() {
        $scope.$apply(function() {
           // do work here, and update the model
        };
      }

      $element.on('click', doSomeWork);
      doSomeWork(); // << this will throw an exception because templates are compiled within $apply
    }
  }
});

```

The fix for the example above looks like this:
```
myApp.directive('myDirective', function() {
  return {
    link: function($scope, $element) {
      function doSomeWork() {
           // do work here, and update the model
      }

      $element.on('click', function() {
        $scope.$apply(doSomeWork); // <<< the $apply call was moved to the callsite that doesn't execute in $apply call already
      });

      doSomeWork();
    }
  }
});

```

To learn more about Angular processing model please check out the {@link guide/concepts concepts doc} as well as the {@link api/ng.$rootScope.Scope api} doc.