Top AngularJS interview questions and answers

AngularJS continues to rise in popularity, and more companies are seeking talented AngularJS developers. More than 6,700 companies, including Google, Amazon, Lyft, Snapchat, and more, report using AngularJS in their tech stacks.

30 AngularJS questions you must prepare for#

Cracking your AngularJS coding interview is crucial to landing one of these coveted roles. To help you prepare, we’ve compiled the essential AngularJS interview questions and answers. This detailed AngularJS interview preparation guide will help you to crack your AngularJS developer interview and secure your next role.

1. What is AngularJS, and its key features?#

AngularJS is a JavaScript framework for building large-scale, single-page web applications (SPAs)A single page application (SPA) is a web application that dynamically updates the content of a single web page without requiring full page reloads.. With AngularJS, you can use HTML as a template language and extend HTML’s syntax to express application components.

AngularJS is known for writing client-side applications with JavaScript and an MVC (Model-View-Controller) model, creating cross-browser compliant applications, and being easy to maintain.

The key features of AngularJS are as follows:

• Testable AngularJS applications
• AngularJS Directives
• AngularJS Services
• AngularJS Scope
• AngularJS Controller

2. What are scopes in AngularJS?#

Scopes in AngularJS act as the glue between the AngularJS controller and the view. They are objects that refer to the application’s model. Scopes are arranged in a hierarchical structure and mimic the DOM structure.

$scope is a built-in object that holds application data and methods. You can create properties of a $scope object inside an AngularJS controller function to manage and access data and functions effectively.

3. What are services in AngularJS?#

In AngularJS, services are the singleton objects or functions that carry out specific tasks across the application. AngularJS services are wired together using dependency injection (DI), allowing developers to organize or share code across an app.

AngularJS includes many built-in services, like $https: service for making HTTP requests and handling API calls. Most AngularJS developers also create custom services to better suit their application needs.

4. Explain the key difference between AngularJS expressions and JavaScript expressions.#

Just like JavaScript, AngularJS expressions are code snippets placed in data binding like {{ expression }}. The most notable differences between AngularJS expressions and JavaScript expressions are:

• In AngularJS, expressions are evaluated within the $scope object, whereas in JavaScript, they are evaluated against the global window object.
• Unlike JavaScript expressions, AngularJS expressions won’t throw errors on null or undefined values.
• Unlike JavaScript expressions, AngularJS expressions do not support loops or conditionals directly, whereas JavaScript expressions can include control structures like loops (for, while) and conditionals (if-else).

5. What are directives in AngularJS?#

Directives are markers on DOM elements that assign new behavior to them. We can use directives to create creative custom HTML tags that work like custom widgets. Directives are arguably the most important component of an AngularJS application.

The most common, built-in directives are:

• ng-model
• ng-repeat
• ng-App
• ng-show
• ng-bind

6. What is data binding in AngularJS?#

In AngularJS, data binding is the automatic data synchronization between the model and view components. The ng-model directive is used for two-way data binding in AngularJS.

This allows you to treat the model as the single source of truth since the view serves as a projection of the model at any given time. This way, the controller and view are totally separate, which improves testing, as you can test your controller in isolation.

7. What is interpolation? Why use it in AngularJS?#

Interpolation in AngularJS is a data-binding technique that allows embedding expressions within text nodes and certain attribute values using double curly braces {{ }}.

During the AngularJS compilation process, the $interpolate service scans for interpolation markup, evaluates embedded expressions, and renders the results in the DOM. If the expressions depend on $scope data, the AngularJS digest cycle ($digest) ensures synchronization by detecting changes and updating the UI accordingly.

8. What is a factory in AngularJS?#

A factory in AngularJS is a simple function that allows developers to add logic to an object and return that object. AngularJS factories can also be used to create reusable functions within the application. When using a factory, it will always return a new instance of that object, making it highly useful for integrating with other AngularJS components like filters or directives.

9. What are the characteristics of scope?#

Scope in AngularJS has five main characteristics:

• Scope provides context against which AngularJS expressions are evaluated.
• To observe model mutations, scopes use the $watch method.
• Scopes provide APIs using $apply that propagate model changes through the system into the view from outside of the realm of controllers, services, or AngularJS event handlers.
• Scope inherits properties from its parent and provides access to shared model properties.
• Scopes can be nested to isolate components.

10. What is dependency injection?#

Dependency injection (DI) is a software design pattern that addresses how AngularJS components handle their dependencies. This pattern relieves a component from finding a dependency and makes them more configurable, reusable, and testable.

Dependency Injection is pervasive throughout AngularJS and can be used either to provide run/config blocks or to define individual components.

AngularJS provides excellent Dependency Injection functionality using the following components:

• Provider
• Value
• Factory
• Constant
• Service

11. How do you integrate AngularJS with HTML?#

To integrate AngularJS with HTML, follow these steps:

1. Include AngularJS JavaScript in the HTML page.

<head>
   <script src = "https://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>
</head>

2. Add the ng-app attribute to the HTML body tag to initiate the AngularJS application.

// example 
<body ng-app = "testapp">
</body>

12. Why do we use double-click in AngularJS?#

The ngDblclick directive in AngularJS allows you to define custom behavior when a double-click event (dblclick) occurs on an HTML element. By using the ngDblclick directive, AngularJS can perform a specified action whenever an element is double-clicked. This directive does not override the element’s native ondblclick event, allowing for seamless double-click event handling.

// example
<button ng-dblclick="count = count + 1" ng-init="count=0">
  Increment (on double click)
</button>
count: {{count}}

The above example shows how AngularJS ngDblclick can be used to increment a value on double-click.

13. How do you reset a $timeout and disable a $watch()?#

To reset a $timeout or $interval() in AngularJS, we must assign the function’s result to a variable. To reset $timeout or $interval(), we use the .cancel() method. Here’s an example:

var customTimeout = $timeout(function () {

}, 55);

$timeout.cancel(customTimeout);

To disable a $watch() in AngularJS, we need to capture the reference of the watcher function when we create it and then call the function to remove the watch.

var unwatch = $scope.$watch('myValue', function(newValue, oldValue) {
    console.log('Value changed from', oldValue, 'to', newValue);
});

// Later in the code, when you want to stop watching:
unwatch();  // This disables the $watch observer

14. What is the digest phase?#

The digest cycle in AngularJS is crucial for data binding. It essentially compares an old and a new version of the same scope model. The digest cycle can be triggered automatically or manually using $apply().

With every digest cycle, each scope model is compared against its previous values. When a change is found, the watches of that model are fired, and another digest cycle is initiated until the data is stable.

This process is not needed if we only use AngularJS core directives. However, if the code has any external changes, the digest cycle needs to be called manually.

15. What is $rootScope, and how does it relate to $scope?#

$rootScope in AngularJS is a scope created on the DOM element that contains the ng-app directive. It acts as a global scope object and is available throughout the entire AngularJS application. An AngularJS application can only have one $rootScope, making it a shared parent scope. Other scopes in AngularJS are considered child scopes of the $rootScope.

16. What is scope hierarchy in AngularJS?#

Each AngularJS application has one root scope ($rootScope) and many child scopes. The scope hierarchy in AngularJS is structured such that when a new scope is created, it is added as a child scope of its parent scope. This creates a hierarchical structure similar to the DOM structure in AngularJS.

The following snippet illustrates the relationship between the root scope and its child scopes within an AngularJS application:

$rootScope
    ├── $scope for myController 1
    └── $scope for myController 2
          └── $scope for childController (child of Controller2)

17. How can you make an AJAX call using AngularJS?#

AngularJS uses the $http service to make AJAX calls. This service enables AngularJS to communicate with a server, which can make a database call to fetch records. Typically, AngularJS handles data in JSON format for such interactions.

function employeeController($scope, $http) {
   var url = "tasks.txt";
   $http.get(url).success(function(response) {
      $scope.employee = response; 
   });
}

The above example demonstrates how to use the $http service in AngularJS for making AJAX requests.

18. What are some common AngularJS Global API functions?#

AngularJS provides several Global API functions under the angular object to perform common type-checking and utility tasks. Some frequently used functions include:

• angular.isNumber(value): Returns true if the provided reference is a numeric value. Useful for number validation.
• angular.isString(value): Returns true if the reference is of type string, helping with string validation.
• angular.isArray(value): Returns true if the reference is an array.
• angular.isFunction(value): Returns true if the reference is a function.
• angular.isObject(value): Returns true if the reference is an object (but not null).

Note: The functions angular.lowercase() and angular.uppercase() were removed in AngularJS 1.5. Instead, use JavaScript’s built-in .toLowerCase() and .toUpperCase().

19. How do you hide an HTML tag?#

You can use the ngHide directive to reveal or hide an HTML element based on specific conditions. By removing or adding the .ng-hide CSS class to the element, you can dynamically control the visibility of the HTML element. The .ng-hide CSS class is predefined in AngularJS.

The .ng-hide class will style an element with display: none !important by default, effectively hiding it from the view. This can be overridden with custom CSS styles if needed, allowing for greater flexibility in your AngularJS applications.

Using the ngHide directive enhances user experience by enabling or disabling elements without manipulating the DOM directly, making it a vital tool for AngularJS developers.

20. Name and describe different phases of the AngularJS Scope life cycle.#

The phases of AngularJS Scope life cycle are as follows:

• Creation: The root scope is created during the initialization of the AngularJS application. This phase establishes the foundation for all other child scopes.

• Model mutation: Directives register watches on the scope that propagate model values to the DOM. This allows for dynamic updates based on user interactions or data changes.

• Watcher registration: Mutations should only be made only within the scope.$apply(). This is done implicitly by AngularJS, ensuring that any changes to the model are properly tracked.

• Mutation observation: After $apply, the $digest cycle starts on the root scope, during which $watched expressions are checked for any model mutations. This phase ensures that the view reflects the current state of the model.

• Scope destruction: The scope creator will destroy unnecessary child scopes using the scope.$destroy() API. Memory used by the child scopes is then reclaimed by the garbage collector, optimizing resource usage in the AngularJS application.

These phases are crucial for managing scope effectively in AngularJS, ensuring efficient data binding and performance.

21. How do you create nested controllers in AngularJS?#

In AngularJS, it is possible to create nested controllers, which allows for a hierarchical structure of $scope variables. Nesting controllers will chain the $scope, meaning changes to the same $scope variable in the parent controller will also affect child controllers.

<div ng-controller="MainCtrl">
  <p>{{msg}} {{name}}!</p>
  
  <div ng-controller="SubCtrl1">
    <p>Hi {{name}}!</p>
    
    <div ng-controller="SubCtrl2">
      <p>{{msg}} {{name}}! Your name is {{name}}.</p>
    </div>
  </div>
</div>

22. Explain the differences between Angular and jQuery. When would you use each?#

jQuery is a lightweight JavaScript library primarily used for DOM manipulation and is ideal for the following use cases:

• HTML and DOM manipulation
• Event handling
• CSS manipulation
• Animation control
• AJAX/JSON support

On the other hand, AngularJS is a powerful JavaScript framework designed for building dynamic web applications. It is best suited for the following use cases:

• Directives as an extension to HTML
• Web application development
• Dependency injection
• Unit testing
• MVC framework support
• Two-way data binding
• RESTful API support

While AngularJS is considered more complex and has a steeper learning curve, jQuery is generally easier to understand for beginners. One of the key advantages of AngularJS is its two-way data binding process, which allows for automatic synchronization between the model and the view. In contrast, jQuery does not support this feature. Additionally, AngularJS provides robust support for deep linking and routing, whereas jQuery lacks built-in capabilities for routing.

In summary, choose jQuery for simple DOM manipulation tasks and quick enhancements, while AngularJS is the better choice for building complex single-page applications (SPAs) and dynamic web interfaces.

23. Which hooks are available in AngularJS? What are their use cases?#

An AngularJS component can implement life cycle hooks, which are essential methods that are called during a component’s life cycle. These hooks allow developers to tap into specific moments in a component’s existence, making it easier to manage state and behavior. The following life cycle hook methods can be implemented in AngularJS:

• $onInit(): This hook is called once the component is initialized, making it useful for setting up initial state or performing one-time setup tasks.
• $onChanges(changesObj): This hook is triggered whenever the component’s bound input properties change. It allows developers to respond to changes in input data, making it ideal for reacting to updates from parent components.
• $doCheck(): This hook provides a mechanism for detecting and responding to changes in the component’s data. It is called after the default change detection mechanism, allowing for custom change detection logic.
• $onDestroy(): This hook is invoked just before a component is destroyed. It’s crucial for cleaning up resources, unsubscribing from services, or stopping timers to prevent memory leaks.
• $postLink(): This hook is executed after the component’s elements have been linked to the DOM. It’s useful for interacting with the DOM or initializing third-party libraries that require the DOM to be fully rendered.

Understanding and utilizing these AngularJS life cycle hooks is vital for effective component management and performance optimization in AngularJS applications.

24. What are pipes in AngularJS?#

Pipes in AngularJS provide a simple method for transforming data within applications. They are versatile functions that can be utilized in template expressions to format and manipulate data dynamically. Pipes take an input value and return a transformed output, making data presentation more flexible and user-friendly.

AngularJS offers several built-in pipes, such as uppercase, lowercase, date, and currency, but developers can also create custom pipes to meet specific application needs. Pipes work by converting data into the specified format, enhancing the user interface of AngularJS applications.

To create and use a pipe, we use the pipe character (|) followed by a filter within a template expression. For example:

<p>Their full name is {{ lastName | uppercase }}</p>

The above code snippet demonstrates how the uppercase pipe transforms the lastName variable to uppercase letters in the rendered output. Utilizing pipes effectively can significantly improve the data presentation and user experience in AngularJS applications.

25. What are isolated unit tests?#

In AngularJS, an isolated unit test involves checking the instance of a class without using injected values or dependencies. Unit testing is a crucial practice in software development, where we are focused on testing individual units of code to ensure they function correctly. To conduct effective software testing, we must isolate the unit we want to test. This approach helps avoid complications, such as making XHR calls to fetch data or interacting with external services.

Isolated unit tests allow developers to independently verify the behavior of specific components or services in AngularJS applications. By mocking dependencies, we can ensure that the tests are focused solely on the logic of the unit being tested, leading to more reliable and maintainable code. Implementing isolated unit tests enhances code quality and helps identify issues early in the development cycle.

26. What is the difference between Angular and AngularJS?#

AngularJS and Angular (2+) are both frameworks developed by Google, but they differ significantly in terms of architecture, performance, and development approach. Here are some key differences:

• Architecture: AngularJS follows an MVC (Model-View-Controller) pattern, while Angular (2+) is built on a component-based architecture that promotes modularity and reusability.
• Language: AngularJS is written in JavaScript, whereas Angular uses TypeScript, a superset of JavaScript that provides better tooling, type safety, and maintainability.
• Performance: Angular delivers better performance and faster rendering due to features like ahead-of-time (AOT) compilation, a virtual DOM, and optimized change detection.
• Data binding: AngularJS primarily relies on two-way data binding, while Angular offers one-way data binding by default and two-way data binding when needed, improving efficiency.
• Dependency injection: Angular has a more structured and modular dependency injection (DI) system, making it easier to manage dependencies across applications.
• Mobile support: AngularJS was designed primarily for desktop applications, while Angular supports both web and mobile development, with optimized performance for modern browsers.

27. How does the angular.Module work?#

The angular.Module is a crucial part of the AngularJS framework, serving as a global container for creating and registering modules. Any modules available to an AngularJS application must be registered with angular.Module to be utilized effectively within the app.

When using angular.Module, passing a single argument will retrieve an existing AngularJS module, while passing multiple arguments creates a new AngularJS module. This functionality allows developers to efficiently organize and manage the application’s components, services, directives, and other dependencies, facilitating better code structure and modular development within the AngularJS ecosystem.

28. What are some ways to improve performance in an AngularJS app?#

There are several methods to enhance the performance of an AngularJS application. Two officially recommended practices for production environments include enabling strict dependency injection (DI) mode and disabling debug data.

Enabling strict DI mode can be achieved by setting it as a directive, like this:

<html ng-app=“myApp” ng-strict-di>

Disabling debug data can be accomplished using the $compileProvider configuration, as shown below:

myApp.config(function ($compileProvider) {
  $compileProvider.debugInfoEnabled(false);
});

In addition to these methods, other popular strategies for improving AngularJS app performance include:

• Utilizing one-time binding (when possible) to minimize unnecessary updates.
• Configuring $httpProvider to use applyAsync for handling HTTP requests more efficiently.

29. What is the difference between an Angular component and a directive?#

An AngularJS component is a specialized type of directive that allows for the utilization of web component functionality throughout an application. With a component, you can effectively divide your AngularJS application into smaller, reusable components. The primary roles of AngularJS components include:

• Declare new HTML via a templateUrl or template
• Create components as part of a component architecture
• Bind view logic to HTML elements
• Define pipes for data transformation

On the other hand, an AngularJS directive is a powerful technique used to attach specific behavior to an element. This enhances the reusability of your components and streamlines the development process. The main roles of AngularJS directives are to:

• Add behavior or extend the existing DOM
• Add existing behavior to an element

30. When a scope is terminated, two destroy events are fired. What are they used for?#

When an AngularJS scope is terminated, two important destroy events are triggered, each serving a distinct purpose in the life cycle of an AngularJS application.

The first event is an AngularJS event called $destroy. This event can be utilized by AngularJS scopes to perform cleanup tasks and remove any associated listeners, ensuring that resources are properly released when a scope is no longer needed.

The second event is a jqLite/jQuery event. This event is fired when a DOM node is removed from the document, allowing developers to handle additional clean-up tasks related to DOM manipulation in their AngularJS applications.

Understanding these destroy events is crucial for effective resource management and ensuring optimal performance in AngularJS development.

15 more questions to explore#

How to prepare for your interview#

Congrats! You’ve made it to the end. Preparing for your AngularJS interview will take time, so be patient with the process. The best way to continue learning AngularJS concepts and improve your skills is to:

• Read and understand the official AngularJS Developer Guide to familiarize yourself with core features and best practices
• Investigate performance issues in AngularJS applications and learn how to articulate effective solutions
• Get hands-on practice with common AngularJS interview questions
• Brush up on your frontend interview skills, including HTML and JavaScript

Mastering AngularJS is just the start. To ace your frontend interview, learn the coding patterns behind every common JavaScript interview question in this FAANG-designed course.

Continue reading about AngularJS, Angular, and frontend coding interviews#

To deepen your knowledge, explore these related blogs:

• Angular vs. AngularJS: What’s the difference?
• 5 tried and true techniques to prepare for a coding interview
• Angular vs. Vue vs. React: Choose the best framework
• 10 JavaScript tips: Best practices to simplify your code