Top 35 Angular Interview Questions and Answers (2024 Edition)

Table of Content

Basic Angular Interview Questions

Q.1 What is Angular and why is it used?

Angular is a platform and framework for building single-page client applications using HTML and TypeScript. It’s used for creating dynamic web applications that can interact with users and provide a seamless experience.

Q.2 What are the key components of Angular?

The key components of Angular include components, templates, directives, services, modules, and dependency injection. These components work together to build a robust and modular application architecture.

The key components of Angular include:

Components: Building blocks of Angular applications that consist of a TypeScript class with a template and styles.
Templates: Declarative views that Angular uses to render the components.
Directives: Extend HTML with behavior or transform the DOM.
Services: Reusable components that provide logic across the application.
Modules: Groups of related components, directives, services, and pipes.
Dependency Injection (DI): A design pattern used to inject dependencies into components or services.

Q.3 How do you set up an Angular application?

To set up an Angular application, you typically use Angular CLI (Command Line Interface) to generate a new project, manage dependencies, and run development servers. After installation, you can scaffold components, services, modules, etc., using CLI commands.

Q.4 What is data binding in Angular? Can you explain the different types of data binding?

Data binding in Angular is the automatic synchronization of data between the model (component) and the view (template). It enables communication between the TypeScript code of the component and the HTML template. There are three types:

Interpolation: {{ data }} – One-way binding from component to view.
Property binding: [property]=”data” – One-way binding from component to view.
Event binding: (event)=”handler” – One-way binding from view to component.

Q.5 What are directives in Angular? Give examples.

Directives in Angular are markers on a DOM element that tell Angular to attach a specified behavior to that DOM element or transform the DOM itself. They are a crucial part of Angular’s declarative syntax and include structural directives like ngIf and ngFor, as well as attribute directives like ngStyle and ngClass.

Q.6 Explain what services are in Angular and why they are used.

Services in Angular are a way to encapsulate and share data, logic, or functionality across components. They help keep components lean by moving business logic out of them, promoting reusability and maintainability.

Q.7 What is dependency injection in Angular?

Dependency Injection (DI) in Angular is a design pattern and framework mechanism for injecting dependencies (services or objects that a class needs to perform its function) into a class rather than the class creating or finding the dependencies itself. It helps manage dependencies and promotes modular design, making components more testable and reusable.

Q.8 How do you handle forms in Angular? Discuss the difference between reactive and template-driven forms.

Handling forms in Angular involves two main approaches:

Template-driven forms: Where the form and its validation logic are mainly defined in the template using directives like ngModel.
Reactive forms: Where form logic is defined programmatically in the component using TypeScript classes to build and manage form controls. Reactive forms offer more flexibility and control over form validation and complex scenarios.

Q.9 What is a module in Angular, and how is it used?

Modules in Angular are a way to organize an application into cohesive blocks of functionality. They group related components, directives, services, and pipes, and are defined with the @NgModule decorator. Modules help with organizing code, managing dependencies, and enabling features like lazy loading.

Q.10 Describe the Angular application architecture.

The Angular application architecture centers around components that interact with services via dependency injection. Components encapsulate views (templates), styles, and business logic, while services provide data and functionality across the application. Modules provide a way to structure and organize the application into functional units.

Q.11 How do Angular applications handle user navigation?

Angular applications handle user navigation through the Angular Router module, which enables navigation between different views and components based on the URL. Routes are defined in the application, and the router matches URLs to routes, loading the corresponding components and updating the view accordingly.

Q.12 What are pipes in Angular? Give examples of commonly used pipes.

Pipes in Angular are a feature that transforms data within a template before displaying it. They allow for formatting data such as dates, numbers, and text dynamically. Examples include DatePipe for date formatting, UpperCasePipe for transforming text to uppercase, and CurrencyPipe for formatting currency values.

Q.13 Explain the concept of a single-page application (SPA). How does Angular facilitate building SPAs?

A single-page application (SPA) is a web application or website that interacts with the user by dynamically rewriting the current page rather than loading entire new pages from the server. Angular facilitates building SPAs through features like the Angular Router for navigation, powerful templating, and data binding capabilities.

Q.14 What is Angular CLI and why is it important?

Angular CLI (Command Line Interface) is a command-line tool provided by Angular for initializing, developing, scaffolding, and maintaining Angular applications. It accelerates development by automating repetitive tasks such as project setup, dependency management, and build configurations, ensuring best practices and consistency across projects.

Q.15 How do you ensure the security of an Angular application?

Ensuring the security of an Angular application involves following secure coding practices such as input validation, protecting against XSS (Cross-Site Scripting) and CSRF (Cross-Site Request Forgery) attacks, using HTTPS for secure communication, and implementing Angular-specific security mechanisms and guidelines provided by the Angular team. Regular updates and adherence to best practices are essential for maintaining a secure Angular application.

Intermediate Angular Interview Questions

Q.16 What are Observables and how are they used in Angular?

Observables are a foundational concept in the RxJS library, which Angular uses for managing asynchronous data, such as data coming from backend services. Observables help in working with a stream of data that can emit multiple values over time. They are used extensively in Angular for handling events, asynchronous HTTP requests, and other asynchronous operations.

Q.17 Explain the lifecycle hooks in Angular components.

Lifecycle hooks are specific functions that allow developers to tap into key moments in a component’s lifecycle, such as creation, rendering, data-bound property changes, and destruction. Common lifecycle hooks include ngOnInit, ngOnChanges, ngAfterViewInit, and ngOnDestroy.

Q.18 How do you implement routing in an Angular application?

Routing in Angular is implemented by configuring a RouterModule in an Angular application. Developers define routes in an AppRoutingModule, associate them with components, and use a <router-outlet> directive in the template to load the component dynamically based on the URL.

Q.19 What are decorators in Angular? Explain a few commonly used decorators.

Decorators are design patterns used to separate modification or decoration of a class without modifying the original source code. In Angular, decorators like @Component, @NgModule, @Injectable, @Input(), and @Output() are commonly used to define components, modules, services, and to handle component interactions.

Q.20 Discuss the use of ngIf, ngFor, and ngSwitch directives.

The *ngIf directive conditionally includes a template based on the truthiness of a specified expression. The *ngFor directive repeats a template for each item in a list. The ngSwitch directive is used for displaying one element from a set based on an expression.

Q.21 How can you communicate between components in Angular?

Communication between components in Angular can be achieved using @Input() and @Output() decorators for parent-child communication, and shared services using @Injectable() for non-direct component communication.

Q.22 What is Angular Material? How do you integrate it into an Angular project?

Angular Material is a UI component library for Angular that provides a wide array of high-quality UI components based on Material Design. It is integrated by installing the package via npm, importing the desired modules from Angular Material into the Angular project’s module file.

Q.23 Explain lazy loading in Angular.

Lazy loading is a design pattern used to delay the loading of object until the point at which it is needed. In Angular, lazy loading is implemented by configuring the RouterModule to load feature modules lazily, which can significantly improve the startup performance of the application.

Q.24 How do you manage state in Angular applications?

State in Angular applications can be managed using services and RxJS libraries, or more sophisticated state management libraries like NgRx or Akita, which offer tools to handle state as a single immutable data structure.

Q.25 What is HttpClient and how do you use it to make API calls?

HttpClient is an Angular service that provides a method of interacting with external web services and APIs over HTTP. It is used to perform GET, POST, DELETE, PUT, and other types of HTTP requests.

Q.26 What are guards in Angular?

Guards in Angular are interfaces that can be implemented to make decisions about routing. Common guards include CanActivate, CanActivateChild, and CanDeactivate, which control navigation to and from routes.

Q.27 How do you handle errors in Angular applications?

Errors in Angular applications can be handled using the catchError operator from RxJS in combination with Angular’s HttpClient, or using global error handling with the ErrorHandler class.

Q.28 What is AOT compilation? How is it different from JIT compilation?

AOT (Ahead-of-Time) compilation converts Angular HTML and TypeScript code into efficient JavaScript code during the build phase, before the browser downloads and runs the code. JIT (Just-in-Time) compilation does this at runtime. AOT improves performance by reducing the app size and boot time.

Q.29 How can you optimize an Angular application’s performance?

Performance can be optimized by using AOT compilation, lazy loading modules, minimizing the use of libraries, keeping track of change detection strategies, and using tools like the Angular DevTools to analyze performance issues.

Q.30 What is Angular Universal, and why would you use it?

Angular Universal is a server-side rendering (SSR) technology for Angular apps. It allows Angular applications to be rendered on the server side, which can help in improving the performance by reducing load times and improving SEO by facilitating web crawlers through the prerendered content.

Advanced Angular Interview Questions

Q.31 Explain the concept of change detection in Angular. How can you optimize it?

Change detection in Angular is a mechanism for tracking changes to data and updating the view to reflect those changes. It can be optimized by using strategies such as OnPush change detection, which limits the framework’s checks to components where input properties change. Additionally, detaching the change detector when a component doesn’t need to be updated or using immutable data structures can further optimize performance.

Q.32 What are dynamic components and how are they implemented in Angular?

Dynamic components in Angular are components that are created and added to the application dynamically at runtime rather than at compile time. They are implemented using Angular’s ComponentFactoryResolver to resolve a component factory for a specific component and then using ViewContainerRef to create and insert an instance of the component into the DOM.

Q.33 Discuss the Dependency Injection pattern in Angular and how it facilitates better testing and modularity.

Dependency Injection (DI) in Angular is a design pattern and core mechanism for resolving dependencies of components, directives, and services. DI enhances modularity by decoupling the creation of a dependency from the class that uses it and facilitates better testing by allowing easy substitution of real services with mock objects.

Q.34 How does Angular work with Web Workers and Server-Side Rendering?

Angular can offload work to Web Workers to run operations in a background thread, keeping the UI responsive. For Server-Side Rendering (SSR), Angular uses Angular Universal, which renders applications on the server, enabling quick first paint and improving SEO by serving rendered pages to bots and crawlers.

Q.35 What are Higher-Order Observables in RxJS? Give examples of how they are used in Angular.

Higher-Order Observables are observables that emit other observables, allowing for complex asynchronous operations to be managed more effectively. In Angular, operations like switchMap, concatMap, mergeMap, and exhaustMap are used to handle scenarios such as canceling in-progress HTTP requests when a new request is made or queuing incoming requests. For example, switchMap is often used in Angular forms to handle auto-complete inputs.