Basic AngularJS Interview Questions for Freshers
AngularJS remains a powerful framework for building dynamic web applications, even as newer frameworks evolve. Preparing for an AngularJS interview requires a deep understanding of its core concepts, directives, services, and more. This comprehensive guide covers AngularJS interview questions for beginners, intermediate, and advanced developers, ensuring you’re ready to ace your next interview. Whether you’re a fresher or an experienced professional, these questions will help you solidify your knowledge and stand out.
Introduction to AngularJS
AngularJS, developed by Google, is a structural framework for dynamic web applications. It uses HTML as a template language and extends its syntax to create reusable components. Despite the rise of Angular (2+), AngularJS (version 1.x) is still widely used in legacy projects, making AngularJS Interview Questions a critical part of technical interviews in 2025.
This guide provides a curated list of questions, answers, and explanations to help you master AngularJS concepts like directives, controllers, services, dependency injection, and more. By understanding these topics, you’ll be better equipped to tackle real-world coding challenges and impress interviewers.
Why AngularJS Interview Questions Matter
Mastering AngularJS interview questions is essential because:
- Legacy Systems: Many organizations maintain AngularJS applications, requiring skilled developers for maintenance and upgrades.
- Foundation for Angular: Understanding AngularJS provides a strong foundation for learning modern Angular versions.
- Demonstrates Versatility: Proficiency in AngularJS showcases your ability to work with both legacy and modern frameworks.
Beginner-Level AngularJS Interview Questions
These questions are designed for candidates new to AngularJS or those preparing for entry-level roles.
1. What is AngularJS, and how does it differ from other JavaScript frameworks?Answer: AngularJS is an open-source JavaScript framework maintained by Google for building single-page applications (SPAs). It uses a Model-View-Controller (MVC) architecture and two-way data binding to simplify development. Unlike jQuery, which focuses on DOM manipulation, AngularJS emphasizes declarative programming and modularity.
Key Difference:
- AngularJS uses directives to extend HTML.
- It supports two-way data binding, unlike React’s one-way binding.
- AngularJS is a full-fledged framework, while libraries like jQuery are more lightweight.
Answer: Two-way data binding automatically synchronizes data between the model and the view. Changes in the view update the model, and vice versa, without explicit DOM manipulation. For example:
<input ng-model=”name”>
<p>{{name}}</p>
If the user types in the input field, the paragraph updates instantly.
3. What are directives in AngularJS?Answer: Directives are markers on DOM elements (e.g., ng-model, ng-repeat) that extend HTML’s functionality. They allow developers to create custom, reusable components. Examples include:
- ng-model: Binds input elements to a model.
- ng-repeat: Iterates over a collection to render lists.
Answer: $scope is an object that acts as a glue between the controller and the view. It holds the model data and functions that the view can access. For example:
app.controller(‘MyController’, function($scope) {
$scope.message = ‘Hello, AngularJS!’;
});
The message variable is accessible in the view via {{message}}.
5. What is dependency injection in AngularJS?Answer: Dependency injection (DI) is a design pattern where dependencies (e.g., services, factories) are injected into components rather than being created inside them. AngularJS’s DI system simplifies testing and modularity. Example:
app.controller(‘MyController’, function($scope, $http) {
// $http is injected
});
6. What is the difference between ng-if and ng-show?Answer:
- ng-if: Removes or adds the DOM element based on the condition. It’s ideal for conditionally rendering elements.
- ng-show: Hides or shows the element using CSS (display: none). The element remains in the DOM.
Example:
<div ng-if=”showDiv”>Visible if true</div>
<div ng-show=”showDiv”>Hidden or shown based on condition</div>
7. What is a module in AngularJS?Answer: A module is a container for controllers, services, directives, and other components. It organizes the application and is created using angular.module(). Example:
var app = angular.module(‘myApp’, []);
8. What is the purpose of ng-app?Answer: The ng-app directive initializes an AngularJS application. It marks the root element of the app and binds it to a specific module. Example:
<div ng-app=”myApp”></div>
9. What are AngularJS expressions?Answer: Expressions are written inside double curly braces {{}} and are used to bind data to the view. They can include variables, operators, or filters. Example:
<p>{{ 5 + 3 }}</p> <!– Outputs 8 –>
10. What is the $rootScope?Answer: $rootScope is the top-level scope for an AngularJS application. All $scope objects inherit from $rootScope. It’s used for data shared across all controllers but should be used sparingly to avoid polluting the global namespace.
Intermediate-Level AngularJS Interview Questions
These questions target developers with some experience in AngularJS, focusing on practical applications and deeper concepts.
11. What is the difference between a service and a factory in AngularJS?Answer:
- Service: A constructor function instantiated by AngularJS using the new keyword. It’s used for sharing utility functions or data.
- Factory: A function that returns an object, giving more control over the object’s creation. Example:
// Service
app.service(‘MyService’, function() {
this.sayHello = function() { return “Hello!”; };
});
// Factory
app.factory(‘MyFactory’, function() {
return {
sayHello: function() { return “Hello!”; }
};
});
12. What is $http service in AngularJS?Answer: The $http service is used to make HTTP requests (GET, POST, etc.) to a server. It returns a promise, allowing asynchronous handling. Example:
$http.get(‘/api/data’).then(function(response) {
$scope.data = response.data;
});
13. Explain the concept of digest cycle in AngularJS.Answer: The digest cycle is AngularJS’s mechanism to monitor changes in $scope variables and update the view. It runs automatically when events like user input or $http responses occur, checking for changes in watched variables and triggering updates.
14. What are filters in AngularJS?Answer: Filters format data for display in the view. AngularJS provides built-in filters like currency, date, and uppercase. Example:
<p>{{ price | currency }}</p> <!– Formats number as currency –>
15. How do you create a custom directive in AngularJS?Answer: Custom directives are created using the directive method. Example:
app.directive(‘myDirective’, function() {
return {
restrict: ‘E’,
template: ‘<div>Custom Directive</div>’
};
});
- restrict: Defines how the directive is used (e.g., E for element, A for attribute).
- template: HTML markup for the directive.
Answer:
- Link: Used for DOM manipulation and event handling. It runs after the template is compiled.
- Controller: Used for directive logic and communication between directives. Example:
app.directive(‘myDirective’, function() {
return {
controller: function($scope) {
$scope.message = ‘Hello’;
},
link: function(scope, element, attrs) {
element.on(‘click’, function() {
alert(scope.message);
});
}
};
});
17. What is $q service in AngularJS?Answer: The $q service provides promises for asynchronous operations. It allows chaining operations and handling success or failure. Example:
var deferred = $q.defer();
deferred.resolve(‘Success’);
deferred.promise.then(function(result) {
console.log(result); // Outputs ‘Success’
});
18. What is the purpose of ngRoute?Answer: ngRoute is a module for client-side routing. It enables navigation between views without full page reloads. Example:
app.config(function($routeProvider) {
$routeProvider
.when(‘/home’, { templateUrl: ‘home.html’, controller: ‘HomeCtrl’ })
.otherwise({ redirectTo: ‘/home’ });
});
19. How do you handle form validation in AngularJS?Answer: AngularJS provides built-in form validation using directives like ng-required, ng-minlength, and ng-pattern. Example:
<form name=”myForm”>
<input ng-model=”user.name” ng-required=”true”>
<span ng-show=”myForm.name.$error.required”>Name is required</span>
</form>
20. What is the $watch function?Answer: The $watch function monitors changes to a $scope variable and triggers a callback when the value changes. Example:
$scope.$watch(‘name’, function(newValue, oldValue) {
console.log(‘Name changed to’, newValue);
});.
Core Concepts of AngularJS Interview Questions
1. Two-Way Data Binding
- What: Automatically synchronizes data between the model (JavaScript variables) and the view (HTML). Changes in the view update the model, and vice versa.
- Why Important: Simplifies UI updates without manual DOM manipulation, a hallmark of AngularJS.
- Key Question: “What is two-way data binding in AngularJS?”
- Example: <input ng-model=”name”> <p>{{name}}</p> – Typing in the input updates the paragraph instantly.
- Interview Tip: Be ready to explain how it differs from one-way binding (e.g., in React) and its performance implications.
2. Directives
- What: Markers on DOM elements (e.g., ng-model, ng-repeat, ng-if) that extend HTML’s functionality, enabling custom behavior or reusable components.
- Why Important: Directives are central to AngularJS’s declarative approach, allowing developers to create dynamic and interactive UIs.
- Key Questions:
- “What are directives in AngularJS?”
- “What is the difference between ng-if and ng-show?”
- “How do you create a custom directive?”
- Example: javascript app.directive(‘myDirective’, function() { return { restrict: ‘E’, template: ‘<div>Custom Directive</div>’ }; });
- Interview Tip: Know the difference between built-in directives (ng-if vs. ng-show) and how to create custom ones using restrict, template, and link.
3. $scope
- What: An object that connects the controller (logic) to the view (UI), holding model data and functions.
- Why Important: Acts as the glue for data binding and is critical for managing application state.
- Key Questions:
- “Explain the role of $scope in AngularJS.”
- “What is $rootScope?”
- Example: javascript app.controller(‘MyController’, function($scope) { $scope.message = ‘Hello, AngularJS!’; });
- Interview Tip: Understand $scope hierarchy and how $rootScope differs (global vs. local scope). Be cautious about overusing $rootScope.
4. Dependency Injection (DI)
- What: A design pattern where dependencies (e.g., services like $http) are injected into components, improving modularity and testability.
- Why Important: AngularJS’s DI system is built-in, making it easier to manage and test components.
- Key Question: “What is dependency injection in AngularJS?”
- Example: javascript app.controller(‘MyController’, function($scope, $http) { $http.get(‘/api/data’).then(function(response) { $scope.data = response.data; }); });
- Interview Tip: Explain how DI enhances code maintainability and how to inject custom services.
5. Services vs. Factories
- What: Services and factories are reusable singleton objects for sharing logic or data. Services use a constructor function, while factories return an object.
- Why Important: Essential for organizing business logic and sharing data across controllers.
- Key Question: “What is the difference between a service and a factory in AngularJS?”
- Example: javascript // Service app.service(‘MyService’, function() { this.sayHello = function() { return “Hello!”; }; }); // Factory app.factory(‘MyFactory’, function() { return { sayHello: function() { return “Hello!”; } }; });
- Interview Tip: Highlight that factories offer more flexibility in object creation, while services are simpler for straightforward logic.
6. Digest Cycle
- What: AngularJS’s mechanism to monitor $scope changes and update the view. It runs automatically for AngularJS events (e.g., ng-click) or manually via $apply.
- Why Important: Understanding the digest cycle is crucial for debugging performance issues and handling asynchronous operations.
- Key Questions:
- “Explain the digest cycle in AngularJS.”
- “What is the difference between $digest and $apply?”
- Example: javascript $scope.$apply(function() { $scope.data = ‘Updated’; });
- Interview Tip: Be prepared to discuss performance optimization, like minimizing watchers to reduce digest cycle overhead.
7. $http Service
- What: A core service for making HTTP requests (GET, POST, etc.) to communicate with servers, returning promises for asynchronous handling.
- Why Important: Essential for fetching or sending data in real-world applications.
- Key Question: “What is the $http service in AngularJS?”
- Example: javascript $http.get(‘/api/data’).then(function(response) { $scope.data = response.data; });
- Interview Tip: Know how to handle success and error cases using promises and explain alternatives like $resource.
8. Filters
- What: Functions that format data for display in the view (e.g., currency, uppercase) or custom logic.
- Why Important: Filters enhance UI presentation and are reusable across the application.
- Key Questions:
- “What are filters in AngularJS?”
- “How do you create a custom filter?”
- Example: javascript app.filter(‘reverse’, function() { return function(input) { return input.split(”).reverse().join(”); }; });
- Interview Tip: Demonstrate knowledge of built-in filters and how to chain them (e.g., {{ data | filter1 | filter2 }}).
9. ngRoute and Client-Side Routing
- What: The ngRoute module enables navigation between views in a single-page application (SPA) without full page reloads.
- Why Important: Routing is critical for building SPAs, a common AngularJS use case.
- Key Question: “What is the purpose of ngRoute?”
- Example: javascript app.config(function($routeProvider) { $routeProvider.when(‘/home’, { templateUrl: ‘home.html’, controller: ‘HomeCtrl’ }); });
- Interview Tip: Compare ngRoute with ui-router and explain when to use each.
10. Performance Optimization
- What: Techniques to improve AngularJS application performance, such as reducing watchers, using one-time binding, or lazy loading.
- Why Important: AngularJS can be slow in large applications, so optimization is a common interview topic.
- Key Question: “How do you optimize AngularJS performance?”
- Example: Use :: for one-time binding: {{ ::name }}.
- Interview Tip: Discuss practical strategies like avoiding complex ng-repeat expressions and using ng-if over ng-show.
Also Read: AngularJS Tutorial
Advanced-Level AngularJS Interview Questions
These questions are for experienced developers and cover complex AngularJS concepts.
21. What is the difference between $digest and $apply?Answer:
- $digest: Processes all watchers in the current scope and its children.
- $apply: Triggers a digest cycle for the entire application and integrates external changes into AngularJS. Example:
$scope.$apply(function() {
$scope.data = ‘Updated’;
});
22. How do you optimize AngularJS performance?Answer: To optimize AngularJS:
- Minimize watchers using one-time binding (::).
- Use ng-if instead of ng-show for conditional rendering.
- Avoid complex expressions in ng-repeat.
- Use $onInit for component initialization.
- Implement lazy loading for large datasets.
Answer:
- ng-model: Enables two-way data binding for form inputs.
- ng-bind: Provides one-way binding for displaying data. Example:
<input ng-model=”name”>
<span ng-bind=”name”></span>
24. How do you handle cross-controller communication?Answer: Use:
- Services: Share data via a singleton service.
- $rootScope: Broadcast events using $rootScope.$broadcast.
- Event Listeners: Use $scope.$on to listen for events. Example:
$rootScope.$broadcast(‘dataUpdated’, data);
$scope.$on(‘dataUpdated’, function(event, data) {
$scope.data = data;
});
25. What is the $location service?Answer: The $location service interacts with the browser’s URL, enabling navigation and URL parsing. Example:
$location.path(‘/new-path’);
26. How do you create a custom filter?Answer: Custom filters are created using the filter method. Example:
app.filter(‘reverse’, function() {
return function(input) {
return input.split(”).reverse().join(”);
};
});
Usage:
<p>{{ ‘Hello’ | reverse }}</p> <!– Outputs ‘olleH’ –>
27. What is the difference between $timeout and $interval?Answer:
- $timeout: Executes a function once after a delay.
- $interval: Repeatedly executes a function at specified intervals. Example:
$timeout(function() { console.log(‘Delayed’); }, 1000);
$interval(function() { console.log(‘Repeated’); }, 1000);
28. How do you implement lazy loading in AngularJS?Answer: Lazy loading can be implemented using libraries like oclazyload. Example:
$ocLazyLoad.load({
name: ‘lazyModule’,
files: [‘lazyModule.js’]
}).then(function() {
$location.path(‘/lazy’);
});
29. What is the $compile service?Answer: The $compile service compiles HTML strings or DOM into AngularJS templates, enabling dynamic content. Example:
var template = ‘<div>{{message}}</div>’;
var compiled = $compile(template)($scope);
element.append(compiled);
30.How do you test AngularJS applications?Answer: Use:
- Jasmine/Karma: For unit testing controllers, services, and directives.
- Protractor: For end-to-end (E2E) testing. Example (Jasmine):
describe(‘MyController’, function() {
it(‘should initialize data’, function() {
expect($scope.data).toBe(‘Initialized’);
});
});
Tips to Prepare for AngularJS Interviews
- Understand Core Concepts: Focus on directives, services, dependency injection, and two-way data binding.
- Practice Coding: Solve real-world problems using AngularJS, such as building a simple SPA.
- Review Legacy Code: Familiarize yourself with AngularJS 1.x syntax, as it differs from Angular (2+).
- Mock Interviews: Practice answering questions with a peer or mentor to build confidence.
- Stay Updated: Although AngularJS is legacy, understanding its integration with modern tools (e.g., Webpack) can be a plus.
SEO Tip: Internal linking to related articles (e.g., “Angular vs. AngularJS”) and external linking to authoritative sources (e.g., AngularJS documentation) can boost rankings.
Conclusion
Preparing for AngularJS interview questions is a crucial step for developers aiming to excel in roles involving legacy systems or transitioning to modern frameworks. This guide covers essential topics, from basic concepts like two-way data binding to advanced topics like $compile and lazy loading. By studying these questions and practicing hands-on coding, you’ll be well-equipped to tackle any AngularJS interview in 2025.
For further learning, explore the official AngularJS documentation or practice building projects to reinforce your skills. Good luck with your interview preparation!