Analyzing Angular.JS with $digest and $apply

With so many interesting features, Angular JS is one of the renowned frameworks for building dynamic web applications. One of the core features is the two-way data binding system that allows automatic data synchronization between the model and its view components. With this powerful creation, one can bring changes in a variable on the $scope object within the view. The object then automatically updates itself with a new value.

Angular JS controls the whole process with different central functions like “$digest()” and “$apply()” to observe the changes in the variable on the $scope object. While writing an expression, Angular JS sets the watcher on the object which further updates the view on the change of the model. Such Angular concepts have greatly simplified the tasks of the programmers.

Let us understand in detail, how these functions work with Angular JS:

Angular.JS with $apply()

$apply() is customized to evaluate the angular expressions outside the context, i.e. DOM event of a third-party library. Once the execution of this function is completed, it calls the $digest to update the $scope objects. When expression $scope.$apply() is executed, it takes a function as a parameter and further called internally to check all the watches.

Angular.JS with $digest()

The function $digest can be used as $scope.$digest() and iterate through all the watches to analyze whether the value has been changed or not. $digest calls the function for each listed item in the $scope model. This function can be called anytime by the Angular JS whenever it is required. However, if the function $digest recognizes any change in the watch list variables, then the event listener will be called to update those variable with the new ones.

When to use $apply() and $digest()?

Functions like $apply() and $digest() are rarely used outside a few instances when $scope object in a directive, needs to update itself. Another case occurs when an object is created for some isolated purpose. Experts recommend not to use $digest/$apply in a controller, as it can make code testing difficult. So, the ideal case to use such functions exists, only when DOM events have triggered outside the Angular JS.

When you are optimizing your application for performance, it is important to understand the life cycle of the angular scope. Dirty checking in Angular JS is used to check whether the value of an expression is changed or not. To know better, about the working of Angular JS and its features, one needs to practice complex codes. For this, you can visit platforms like CodeFights. It not only helps you in resolving the complex errors but also let's you do programming Interview Practice to apply for tech jobs. Get the best programming questionnaire and coding challenges for your technical advancement and future growth. Visit CodeFights today!