Receiving Console Error When Attempting to Implement ngClass Directive Within Another Directive

Question

Receiving Console Error When Attempting to Implement ngClass Directive Within Another Directive

I have encountered a console error while trying to utilize ngClass within my directive. The specific error message reads:

Error: [$rootScope:infdig] 10 $digest() iterations reached. Aborting!

To demonstrate this issue, here is a simplified version of the directive causing the problem:

angular.module('myApp', [])
    .directive('myDirective', function () {
    return {
        restrict: 'E',
        scope: {
            myNgClass: '='
        },
        template: '<div ng-class="myNgClass">Hello World</div>'
    }
});

Furthermore, I am implementing the directive in the following manner:

<my-directive my-ng-class="{'green':true}"></my-directive>

You can also access a related jsFiddle link.

javascript angularjs angularjs-directive

Answer 1

Answer №1

First and foremost, this issue is specific to the version of Angular being used (v1.2.1) - it was resolved in v1.2.5 (see demo with v1.2.5).

Secondly, it is advisable not to utilize two-way binding ("=") if there is no need to modify the value from within the directive. Unnecessarily using "=" creates 2 watchers.

Instead, opt for one-way string binding ("@"), like this:

scope: {
  myNgClass: '@'
},
template: '<div ng-class="{{myNgClass}}">Hello World</div>'

However, bear in mind that this approach has limited functionality. For instance, passing an object (

$scope.greenStyle = { green: true };

) to the directive won't work as expected:

<my-directive my-ng-class="greenStyle"></my-directive>

It's more effective to use a one-way binding to expressions - "&". This method maintains a single watch and binds to an object instead of a string. The scope.myNgClass now acts as a function returning the value of the bound expression:

scope: {
  myNgClass: '&'
},
template: '<div ng-class="myNgClass()">Hello World</div>'

View Demo

Answer 2

First and foremost, this issue is specific to the version of Angular being used (v1.2.1) - it was resolved in v1.2.5 (see demo with v1.2.5).

Secondly, it is advisable not to utilize two-way binding ("=") if there is no need to modify the value from within the directive. Unnecessarily using "=" creates 2 watchers.

Instead, opt for one-way string binding ("@"), like this:

scope: {
  myNgClass: '@'
},
template: '<div ng-class="{{myNgClass}}">Hello World</div>'

However, bear in mind that this approach has limited functionality. For instance, passing an object (

$scope.greenStyle = { green: true };

) to the directive won't work as expected:

<my-directive my-ng-class="greenStyle"></my-directive>

It's more effective to use a one-way binding to expressions - "&". This method maintains a single watch and binds to an object instead of a string. The scope.myNgClass now acts as a function returning the value of the bound expression:

scope: {
  myNgClass: '&'
},
template: '<div ng-class="myNgClass()">Hello World</div>'

View Demo

Answer 3

Answer №2

Replace using @ instead of =.

myNgClass: '@'

When you opt for =, angular sets up a $watch for changes to 'myNgClass'. Adding a $watch leads anguar to include $$hashKey to the object and "tries" to assign back the modified object to its original source (ensuring both have the same object).

The issue arises during $digest comparison where it has

{'green':'true', $$hashKey: '123546246'}

against the evaluated expression {'green':'true'}. This results in a failed comparison triggering the $watch listener (NOTE: This is just a theory. I am not completely certain about the addition of hashKey, but what I do know is that it considers the objects as distinct instances causing the watch listener to trigger). As my-ng-class always returns a new instance of that object, it will always be unique and thus activate the watch listener.

If you still prefer using = (though there's no necessity), you simply need to define your initial object once elsewhere before passing it through. You can use ng-init for this purpose, like so:

<my-directive ng-init="clazz={'green':'true'}" my-ng-class="clazz"></my-directive>

Answer 4

Replace using @ instead of =.

myNgClass: '@'

When you opt for =, angular sets up a $watch for changes to 'myNgClass'. Adding a $watch leads anguar to include $$hashKey to the object and "tries" to assign back the modified object to its original source (ensuring both have the same object).

The issue arises during $digest comparison where it has

{'green':'true', $$hashKey: '123546246'}

against the evaluated expression {'green':'true'}. This results in a failed comparison triggering the $watch listener (NOTE: This is just a theory. I am not completely certain about the addition of hashKey, but what I do know is that it considers the objects as distinct instances causing the watch listener to trigger). As my-ng-class always returns a new instance of that object, it will always be unique and thus activate the watch listener.

If you still prefer using = (though there's no necessity), you simply need to define your initial object once elsewhere before passing it through. You can use ng-init for this purpose, like so:

<my-directive ng-init="clazz={'green':'true'}" my-ng-class="clazz"></my-directive>

Receiving Console Error When Attempting to Implement ngClass Directive Within Another Directive

Answer №1

Answer №2

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