30 Advanced Angular Interview Questions and Answers
By admin | 9 months ago
1. How does Angular's Change Detection mechanism work under the hood?
Answer: Angular's Change Detection mechanism checks for changes in the data model and updates the DOM to reflect these changes. It uses zones to intercept asynchronous activities and runs change detection following these events. The default strategy checks every component from top to bottom in the component tree, but developers can optimize performance by using the `OnPush` change detection strategy, which limits the checks to components that have received new references to their inputs.
2. Can you explain the concept of Zone.js in Angular?
Answer: Zone.js is a library that Angular uses to wrap and monitor asynchronous operations in the application (like setTimeout, Promise). It helps in automatically triggering Angular's change detection whenever an async operation occurs by notifying Angular of the start and completion of these operations, facilitating the automatic application of changes to the view.
3. What are Dynamic Components and how are they used in Angular?
Answer: Dynamic Components are components that are created and added to the application at runtime rather than at compile time. Angular provides a way to dynamically load components using the `ViewContainerRef` and `ComponentFactoryResolver` classes. This is particularly useful for scenarios like loading components based on user actions or when implementing complex UI structures such as modals or tabs dynamically.
4. Explain the concept of Content Projection in Angular.
Answer: Content Projection (previously known as Transclusion in AngularJS) allows developers to create components that can accept and render external HTML content inside their templates. It is implemented using the `
5. How do you implement internationalization (i18n) in an Angular application?
Answer: Angular supports internationalization (i18n) through the use of locale identifiers to translate text in templates. Developers can use the Angular CLI to extract text into translation files, which can then be translated into different languages. The application can then load the appropriate translations based on the user's locale. Angular also supports formatting numbers, dates, and currencies according to the locale.
6. Describe the process of server-side rendering with Angular Universal.
Answer: Server-side rendering (SSR) with Angular Universal involves rendering Angular applications on the server and serving them as static HTML to the browser. This approach improves the performance and SEO of Angular applications by reducing the time to first contentful paint. It involves setting up an Angular Universal server that handles rendering and serving the application for specific routes.
7. What is the role of the `@HostListener` and `@HostBinding` decorators?
Answer: The `@HostListener` decorator allows you to listen to events on the host element of the directive/component. `@HostBinding` allows you to bind properties to the host element. These decorators are useful for interacting directly with the DOM to add event listeners or bind properties without modifying the component's template.
8. How do you use Web Workers in Angular and why?
Answer: Web Workers allow Angular applications to run scripts in background threads, offloading work from the main thread to enhance performance, especially in computationally intensive tasks. Angular CLI provides support for integrating Web Workers by generating the necessary boilerplate code to facilitate communication between the main thread and the worker.
9. Explain the difference between Observables and Promises in Angular.
Answer: Observables and Promises both handle asynchronous operations, but Observables support multiple values over time, can be canceled, and support operators like map, filter, reduce, etc., making them more powerful for complex asynchronous tasks. Promises, however, handle a single event and cannot be canceled once initiated.
10. How does Angular handle security concerns like XSS?
Answer: Angular provides built-in protection against XSS (Cross-Site Scripting) by automatically escaping user input values displayed in the template. For dynamic content, developers should use the `DomSanitizer` service to sanitize content explicitly before adding it to the DOM.
11. Describe the use of the `async` pipe in Angular.
Answer: The `async` pipe subscribes to an Observable or Promise and returns the latest value it has emitted. When the component gets destroyed, the `async` pipe unsubscribes automatically to avoid potential memory leaks.
12. How can you manage state in Angular applications?
Answer: State in Angular applications can be managed using services with BehaviorSubjects or by integrating state management libraries such as NgRx, which provides tools for managing global and local state in a reactive way using the principles of Redux.
13. What is the Angular Ivy compiler and why is it important?
Answer: Angular Ivy is the code name for Angular's next-generation compilation and rendering pipeline. It provides faster compilation, smaller bundle sizes, and improved debugging. Ivy's architecture is designed to be more incremental and enables new features like lazy loading of component styles.
14. How do you use interceptors in Angular?
Answer: Interceptors are used in Angular to intercept incoming or outgoing HTTP requests using the HttpClient. They are useful for tasks like adding authentication tokens to requests, logging, or handling errors globally.
15. What are the advantages of using Angular Material?
Answer: Angular Material provides a set of reusable UI components based on Material Design principles. Advantages include consistency in UI, accessibility, responsiveness, and ease of use, which accelerates development.
16. Explain the use of the `ng-container` directive.
Answer: The `ng-container` directive acts as a grouping element for structural directives (like *ngIf, *ngFor) that doesn't interfere with styles or layout because it doesn't get rendered in the DOM.
17. How do you create a custom structural directive in Angular?
Answer: To create a custom structural directive, you define a directive that manipulates the DOM by adding or removing elements. This involves using the `TemplateRef` and `ViewContainerRef` to embed or clear a template.
18. Describe the process of form validation in Angular.
Answer: Angular provides two approaches to form validation: template-driven and reactive forms. Both support standard validation attributes (like required, minlength, maxlength) and custom validators. Validation logic can be triggered on form submission or in real-time as the user interacts with the form.
19. What is the difference between `mergeMap, switchMap, and concatMap` in RxJS?
Answer: These RxJS operators are used for handling observable sequences:
-
mergeMap: Projects each source value to an Observable and merges them into a single Observable. -
switchMap: Projects each source value to an Observable, but if a new value arrives, it will switch to the new Observable by canceling the previous one. -
concatMap: Projects each source value to an Observable and concatenates them, waiting for each one to complete before starting the next.
20. How do you optimize Angular application performance?
Answer: Performance can be optimized by using strategies like lazy loading of modules, implementing the OnPush change detection strategy, optimizing bundle sizes using tree-shaking, using trackBy with *ngFor, and avoiding unnecessary computations in templates.
21. What is AOT compilation, and how does it differ from JIT compilation?
Answer: 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. This differs from JIT (Just In Time) compilation, which compiles the application in the browser at runtime. AOT improves performance and security by reducing the application's load time and size.
22. Explain the concept of dependency injection in Angular.
Answer: Dependency Injection (DI) is a design pattern used by Angular to provide components with the dependencies (services or objects) they need to perform their functions. DI decouples the creation of dependent objects from the class that uses them, making the application more modular and easier to test.
23. What are Angular modules and their purpose?
Answer: Angular modules (NgModule) help organize an application into cohesive blocks of functionality. Each module is a standalone unit that can contain components, directives, pipes, and services. Modules can be eagerly loaded or lazily loaded to optimize application performance.
24. How do you handle routing in Angular?
Answer: Routing in Angular is handled by the RouterModule, which allows the definition of navigation paths, lazy-loading of modules, and handling parameters and guards to protect routes. It provides a way to manage navigation from one view to the next as users perform application tasks.
25. Explain how to use the `RouterOutlet` directive.
Answer: The `RouterOutlet` directive acts as a placeholder that Angular dynamically fills based on the current router state. It is where the routed component gets displayed. Multiple outlets can be named and used for secondary routes.
26. How do you implement lazy loading of modules in Angular?
Answer: Lazy loading in Angular is implemented by configuring the RouterModule to asynchronously load a module only when it is needed for a particular route. This is achieved by using the `loadChildren` property in the route configuration, specifying the module to be lazily loaded.
27. Describe the lifecycle hooks of Angular components.
Answer: Angular components have several lifecycle hooks that allow execution of code at specific points in a component's lifecycle: ngOnInit, ngOnChanges, ngDoCheck, ngAfterContentInit, ngAfterContentChecked, ngAfterViewInit, ngAfterViewChecked, and ngOnDestroy.
28. How do you communicate between components in Angular?
Answer: Components can communicate using Input/Output properties for parent-child communication, Services for shared data, or advanced techniques like Observables for cross-component communication.
29. What is the purpose of the `ngDoCheck` lifecycle hook?
Answer: The `ngDoCheck` lifecycle hook is called to detect and act upon changes that Angular can't or won't detect on its own. It's a way for developers to implement custom change detection for components.
30. How do you secure Angular applications against CSRF or XSRF attacks?
Answer: Angular has built-in support to protect against CSRF/XSRF attacks by utilizing tokens that are automatically added to HTTP requests through the HttpClient. Developers should ensure that their backend checks these tokens to validate requests.
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