Angular Developer Interview Questions
Angular's two-way data binding and component-based architecture have made it a go-to for modern web applications. This article helps hiring managers discern the best from the rest with its curated set of Angular-centric interview questions. Assess a candidate's skills in SPA design, dependency injection, and more, ensuring they're adept at creating dynamic and efficient web applications.
What is Angular, and how does it differ from AngularJS?
Answer: Angular is a platform and framework for building client-side applications with HTML, CSS, and TypeScript. AngularJS refers to the 1.x versions of the framework, while Angular refers to Angular 2 and beyond.
2.
Explain the architecture of an Angular application.
Answer: Angular apps are modular and are composed of modules, components, services, directives, and templates. The main building blocks are modules and components.
3.
What are Angular Modules?
Answer: Angular Modules (or NgModules) are containers for a cohesive block of code dedicated to an application domain, a workflow, or a set of related capabilities.
4.
What are directives in Angular?
Answer: Directives are classes that modify the structure of the DOM or its behavior. There are three types: components, structural directives, and attribute directives.
5.
Explain the difference between one-way and two-way data binding.
Answer: One-way data binding binds the data from the component to the view (or vice versa), while two-way data binding ensures synchronization between the view and the component model.
6.
What is the purpose of Angular services?
Answer: Services in Angular are singleton objects that get instantiated only once during the lifetime of an application. They contain methods that maintain data throughout the application, such as fetching data from the server.
7.
Describe the Angular Component Lifecycle.
Answer: Angular components go through a life cycle, which includes stages like creation, rendering, binding, and destruction. Lifecycle hooks like ngOnInit, ngOnChanges, and ngOnDestroy help in managing these stages.
8.
How does Angular handle forms?
Answer: Angular provides two approaches: template-driven forms and reactive forms. The former relies on directives, while the latter uses reactive patterns and is more scalable.
9.
What is Dependency Injection in Angular?
Answer: Dependency Injection (DI) is a design pattern where a class receives its dependencies from an external source. Angular has its DI framework, which helps in maintaining modularity and efficiency.
10.
What is the async pipe?
Answer: The async pipe subscribes to an Observable or Promise, returns the latest value it emitted, and automatically unsubscribes when the component is destroyed.
11.
How do you handle API calls in Angular?
Answer: Angular provides the HttpClient module to make API calls. Services typically manage these calls, and Observables handle the asynchronous nature of HTTP requests.
12.
Describe the differences between @ViewChild and @ViewChildren.
Answer: @ViewChild provides the first element or directive matching the selector, whereas @ViewChildren provides all elements or directives that match the selector.
13.
What is AOT (Ahead-of-Time) compilation in Angular?
Answer: AOT compiles Angular components and templates to native JavaScript and HTML during the build phase, before the browser downloads and runs the code, improving runtime performance.
14.
How can you handle errors in Angular?
Answer: Error handling can be done using services like ErrorHandler and methods like catchError within RxJS.
15.
What are Angular Guards?
Answer: Guards are interfaces that determine navigation to a route. They can decide if a route can be activated, deactivated, or even loaded.
16.
What's the difference between an Observable and a Promise?
Answer: Both deal with asynchronous operations. Observables can emit multiple values over time, are cancellable, and offer operators like map and filter. Promises resolve a single value and are not cancellable.
17.
Explain the role of the ngZone service.
Answer: ngZone provides an execution context for tracking and triggering change detection in Angular applications. It helps in integrating third-party code with Angular's change detection mechanism.
18.
Describe lazy loading in Angular.
Answer: Lazy loading is a technique that allows Angular to load feature modules on demand to boost performance. It loads parts of the app as required rather than loading everything upfront.
19.
What are Angular Interceptors?
Answer: Interceptors allow developers to intercept HTTP requests and responses to transform or handle them before passing them along. They're often used for authentication, logging, or caching.
20.
How do you ensure state management in Angular?
Answer: While Angular doesn't have built-in state management, libraries like NgRx or Akita can be integrated for a redux-style state management solution.
21.
How do you share data between components?
Answer: Data can be shared using @Input() and @Output() decorators, through services, or using state management libraries.
22.
What is Angular Universal?
Answer: Angular Universal is a technology for server-side rendering of Angular applications. It improves performance and helps in SEO optimization.
23.
Explain the differences between switchMap, mergeMap, concatMap, and exhaustMap.
Answer: These are RxJS operators for higher-order observables. switchMap cancels previous inner subscriptions, mergeMap merges multiple observables, concatMap maintains the order, and exhaustMap ignores new items if the previous one is still processing.
24.
What's the difference between a resolver and a guard in Angular's routing?
Answer: While both relate to routing, guards determine if a route can be activated or loaded, whereas resolvers perform route data retrieval before route activation.
25.
How can you optimize the performance of an Angular application?
Answer: Some methods include using the ChangeDetectionStrategy.OnPush, lazy loading modules, implementing AOT compilation, using trackBy in ngFor, and optimizing observables with operators like shareReplay.
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