Top 75+ AngularJS Interview Questions and Answers for 2024

AngularJS, a popular open-source JavaScript framework developed and maintained by Google, is widely used for building single-page applications (SPAs). As AngularJS continues to gain traction in the web development world, many companies are actively seeking skilled AngularJS developers. If you’re preparing for an AngularJS interview, it’s essential to be well-versed in the framework’s concepts, features, and best practices. In this article, we’ll cover 75+ AngularJS interview questions and answers to help you ace your next interview.

What is AngularJS?

AngularJS is a structural framework for dynamic web applications. It extends HTML with new attributes and provides a way to create and manage web applications. AngularJS simplifies the development process by handling tasks such as data binding, scope management, and DOM manipulation, allowing developers to focus on building the application logic.

How does AngularJS work?

AngularJS works based on the Model-View-Controller (MVC) architectural pattern. It separates the application logic from the user interface, making it easier to manage and maintain complex web applications. The MVC pattern in AngularJS is implemented as follows:

• Model: Represents the data and business logic of the application.
• View: Refers to the HTML template that displays the data to the user.
• Controller: Contains the logic for handling user interactions and updating the model.

Key Features of AngularJS

• Data Binding: AngularJS provides two-way data binding, which automatically synchronizes the model data with the view, eliminating the need for manual DOM manipulation.
• Dependency Injection: AngularJS supports dependency injection, making it easier to create and manage reusable components.
• Directives: AngularJS provides a way to extend HTML with custom directives, which can encapsulate complex functionality and improve code organization.
• Templates: AngularJS uses HTML templates, allowing developers to define the structure and layout of the application’s user interface.
• Routing: AngularJS includes a built-in routing mechanism, making it easy to create single-page applications with multiple views.
• Testing: AngularJS provides built-in support for unit testing, making it easier to write and maintain testable code.

Top AngularJS Interview Questions and Answers

1. What is AngularJS?

AngularJS is a structural framework for dynamic web applications. It extends HTML with new attributes and provides a way to create and manage web applications.

2. What is the difference between AngularJS and Angular?

AngularJS is the original version of the framework, while Angular is a complete rewrite of AngularJS. Angular is a more modern, modular, and performance-optimized version of the framework. However, AngularJS is still widely used and maintained by the Angular team.

3. What is the purpose of the ng-app directive?

The ng-app directive is used to initialize an AngularJS application and define the root element of the application. It automatically bootstraps the application and attaches the AngularJS event handlers to the specified element and its children.

4. Explain the concept of data binding in AngularJS.

Data binding is a mechanism that synchronizes the data between the model and the view components in AngularJS. AngularJS provides two types of data binding:

• One-way data binding: Updates the view when the model changes, but not vice versa.
• Two-way data binding: Synchronizes changes between the model and the view in both directions.

5. What is the purpose of the ng-model directive?

The ng-model directive is used to bind input elements (such as text boxes, dropdowns, and checkboxes) to a property in the scope, enabling two-way data binding. It allows the user’s input to be automatically reflected in the model and vice versa.

6. What are directives in AngularJS?

Directives are markers (such as attributes, elements, or comments) in AngularJS that extend the HTML and add behavior to the DOM elements. Directives provide a way to create reusable components and encapsulate complex functionality.

7. What is the difference between a service and a factory in AngularJS?

Both services and factories are used to create reusable components in AngularJS, but they differ in their implementation.

• Service: A service is a singleton object that holds some data or logic. It is instantiated using the new keyword and can have methods and properties.
• Factory: A factory is a function that returns an object. It is used to create objects or functions, and the returned value can be a constructor function or a plain object.

8. Explain the concept of dependency injection in AngularJS.

Dependency injection is a design pattern that allows objects to receive their dependencies from an external source rather than creating them internally. AngularJS provides built-in support for dependency injection, making it easier to create and manage reusable components.

9. What is the purpose of the ng-repeat directive?

The ng-repeat directive is used to iterate over a collection (array or object) and generate a new instance of the directive’s host element for each item in the collection. It is commonly used to display lists or tables of data in the view.

10. What is the purpose of the ng-click directive?

The ng-click directive is used to bind an expression or a function to an element’s click event. It allows you to execute AngularJS expressions or functions when the user clicks on the element.

11. How can you share data between controllers in AngularJS?

There are several ways to share data between controllers in AngularJS:

• Services: Create a shared service that can be injected into multiple controllers.
• Events: Use the $broadcast, $emit, and $on methods to communicate between controllers via events.
• Parent-child hierarchy: Use a parent controller to pass data to its child controllers through scope inheritance or bindings.
• Third-party libraries: Use libraries like ngStorage or ngCookies to store and retrieve data across controllers.

12. What is the purpose of the ng-show and ng-hide directives?

The ng-show and ng-hide directives are used to conditionally show or hide elements based on a given expression.

• ng-show: Shows the element when the expression is truthy.
• ng-hide: Hides the element when the expression is truthy.

13. How can you create a custom directive in AngularJS?

To create a custom directive in AngularJS, you can use the directive method provided by the AngularJS module. Here’s an example:

angular.module('myApp', [])  .directive('myDirective', function() {    return {      restrict: 'E', // Use 'E' for an element directive      template: '<div>This is a custom directive</div>'    };  });

You can then use the custom directive in your HTML like this:

<my-directive></my-directive>

14. What is the purpose of the $scope object in AngularJS?

The $scope object is a crucial concept in AngularJS. It acts as a glue between the controller and the view, providing a way to pass data and functions from the controller to the view and vice versa. The $scope object is a hierarchical structure that follows the DOM tree structure, allowing for inheritance and prototypal scope inheritance.

15. Explain the concept of digest cycle in AngularJS.

The digest cycle is the process by which AngularJS detects changes in the model and propagates those changes to the view. AngularJS continuously watches for changes in the model and updates the view accordingly. The digest cycle runs automatically, but it can also be triggered manually using the $apply() method in cases where AngularJS is not aware of the changes made outside its context (e.g., browser events).

16. What is the purpose of the $watch function in AngularJS?

The $watch function is used to watch for changes to a model property or an expression. It allows you to execute a callback function whenever the watched expression changes. This is useful for performing actions or updating the view based on model changes.

$scope.$watch('expression', function(newValue, oldValue) {  // Code to execute when the expression value changes});

17. What is the difference between ng-if and ng-show/ng-hide?

The ng-if directive is used to conditionally render or remove elements from the DOM based on an expression. If the expression is falsy, the element is removed from the DOM, and if it’s truthy, the element is added to the DOM.

On the other hand, ng-show and ng-hide directives toggle the visibility of an element by setting the display CSS property to none or block, respectively. The element remains in the DOM regardless of the expression’s value.

Using ng-if is generally preferred over ng-show/ng-hide when dealing with large templates or collections, as it avoids unnecessary rendering and improves performance.

18. How can you create a custom filter in AngularJS?

You can create a custom filter in AngularJS by using the filter method provided by the AngularJS module. Here’s an example:

angular.module('myApp', [])  .filter('myFilter', function() {    return function(input, arg1, arg2) {      // Filter logic goes here      return transformedInput;    };  });

You can then use the custom filter in your HTML like this:

{{ data | myFilter:arg1:arg2 }}

19. What is the purpose of the $http service in AngularJS?

The $http service is a core AngularJS service used for making HTTP requests to a server. It provides a clean and straightforward way to perform AJAX requests, handle responses, and handle errors. The $http service returns a promise, which allows for asynchronous handling of responses.

20. How can you implement routing in an AngularJS application?

AngularJS provides built-in support for routing through the ngRoute module. To implement routing, you need to:

1. Include the ngRoute module in your application.
2. Define routes using the $routeProvider service.
3. Use the ng-view directive to specify where the rendered template should be placed.

Here’s an example of defining a route:

angular.module('myApp', ['ngRoute'])  .config(function($routeProvider) {    $routeProvider      .when('/home', {        templateUrl: 'views/home.html',        controller: 'HomeController'      })      .otherwise({        redirectTo: '/home'      });  });

21. What is the purpose of the $q service in AngularJS?

The $q service is a helper service that provides a way to work with promises in AngularJS. Promises are used to handle asynchronous operations, such as HTTP requests or delayed operations. The $q service provides methods for creating, chaining, and handling promises, making it easier to manage asynchronous code.

22. How can you implement form validation in AngularJS?

AngularJS provides built-in support for form validation through the ngModel directive and various validation directives like required, minlength, maxlength, pattern, and more. You can also create custom validation directives or use third-party libraries like ngMessages for more advanced form validation scenarios.

Here’s an example of a simple form validation:

<form name="myForm" novalidate>  <input type="text" name="userName" ng-model="user.name" required>  <span ng-show="myForm.userName.$error.required">Name is required.</span></form>

23. How can you handle exceptions and errors in AngularJS?

AngularJS provides an exception handling mechanism through the $exceptionHandler service. You can override the default behavior of this service to handle exceptions in a custom way, such as logging errors or displaying error messages to the user.

Here’s an example of overriding the $exceptionHandler service:

angular.module('myApp', [])  .factory('$exceptionHandler', function($log) {    return function(exception, cause) {      $log.error('Exception: ', exception);      $log.error('Cause: ', cause);      // Additional error handling logic    };  });

24. What is the purpose of the $rootScope in AngularJS?

The $rootScope is the topmost scope in the AngularJS scope hierarchy. It serves as a global scope, meaning that any properties or methods defined on the $rootScope are available throughout the entire application. However, it’s generally recommended to use services or other mechanisms for sharing data across components instead of relying heavily on the $rootScope.

25. How can you implement a custom service in AngularJS?

You can create a custom service in AngularJS by using the service method provided by the AngularJS module. Here’s an example:

angular.module('myApp', [])  .service('myService', function() {    this.myData = 'Initial data';    this.myMethod = function() {      // Service logic    };  });

You can then inject the service into your controllers or other components:

angular.module('myApp', [])  .controller('MyController', function(myService) {    // Use myService  });

Conclusion

Mastering AngularJS requires a deep understanding of its concepts, features, and best practices. These 75+ AngularJS interview questions and answers cover a wide range of topics, from fundamental concepts like data binding and directives to more advanced topics like routing, form validation, and custom services.

By thoroughly preparing for these questions, you’ll not only increase your chances of acing the AngularJS interview but also solidify your understanding of the framework. Remember, practice is key, so make sure to implement these concepts in your own projects or coding exercises to gain hands-on experience.

Good luck with your AngularJS interview preparation!