Http & Apis Interview Questions

HttpClient is Angular's built-in HTTP client. Features: typed responses, observables for requests, interceptors support, progress events, error handling. Provides methods for HTTP operations (get, post, put, delete). Supports request/response transformation.

Interceptors intercept and modify HTTP requests/responses. Use cases: authentication headers, error handling, loading indicators, caching, logging. Implement HttpInterceptor interface. Can be chained, order matters.

Error handling through catchError operator, error interceptors. Implement global/local error handlers, retry logic. Consider error types (network, server, client), user feedback. Use ErrorHandler class for global handling.

Best practices: separate service layer, typed interfaces, proper error handling, environment configuration. Consider request caching, retry strategies, cancellation. Implement proper separation of concerns.

Caching implemented through interceptors, services. Use shareReplay operator, cache storage. Consider cache invalidation, freshness checks. Important for performance optimization, offline support.

HttpParams manage URL parameters in requests. Immutable object for query parameters. Methods: set(), append(), delete(). Important for API queries, filtering. Consider parameter encoding, multiple values.

File uploads using FormData, multipart/form-data content type. Support progress events, cancellation. Consider file size limits, validation. Implement proper error handling, progress tracking.

Request cancellation using takeUntil operator, AbortController. Implement cleanup on component destruction. Important for preventing memory leaks, unnecessary requests. Consider loading states.

Authentication through interceptors, auth headers. Implement token management, refresh logic. Consider session handling, secure storage. Important for secured APIs, user sessions.

Headers managed through HttpHeaders class. Set content type, authorization, custom headers. Immutable object, chainable methods. Consider CORS, security headers. Important for API communication.

Retry logic using retry/retryWhen operators. Configure retry count, delay. Consider error types, backoff strategy. Important for handling temporary failures, network issues.

Progress events track upload/download progress. Use reportProgress option, HttpEventType. Implement progress indicators, cancellation. Important for large file operations, user feedback.

Concurrent requests using forkJoin, combineLatest operators. Consider error handling, loading states. Important for dependent data, parallel operations. Implement proper request management.

CORS (Cross-Origin Resource Sharing) handled through server configuration, proxy settings. Configure allowed origins, methods, headers. Consider security implications, browser restrictions. Important for cross-domain requests.

API versioning through URL prefixes, headers, interceptors. Configure base URLs, version management. Consider backward compatibility, migration strategy. Important for API evolution.

Timeouts configured using timeout operator, request configuration. Consider network conditions, server response time. Important for user experience, error handling. Implement proper feedback.

Offline support through service workers, local storage. Implement queue system, sync logic. Consider conflict resolution, data persistence. Important for offline-first applications.

Response types: json, text, blob, arrayBuffer. Configure using responseType option. Consider data format, transformation needs. Important for different content types, file downloads.

API mocking through interceptors, mock services. Configure development environment, test data. Consider realistic scenarios, error cases. Important for development, testing.

Security considerations: XSS prevention, CSRF protection, secure headers. Implement authentication, authorization. Consider data encryption, input validation. Important for application security.

Large data handling through pagination, infinite scroll. Implement virtual scrolling, data chunking. Consider performance impact, memory usage. Important for scalable applications.

Debouncing delays request execution until pause in triggering. Implement using debounceTime operator. Consider user input, search functionality. Important for performance optimization.

Error mapping through interceptors, error services. Transform server errors to application format. Consider error categorization, localization. Important for consistent error handling.

WebSockets enable real-time communication. Implement using socket.io, custom services. Consider connection management, reconnection logic. Important for real-time features.

Rate limiting through interceptors, request queuing. Implement backoff strategy, request prioritization. Consider server limits, user experience. Important for API consumption.

Transformation through interceptors, map operator. Modify request/response data format. Consider data consistency, type safety. Important for API integration.

Request queueing through custom services, RxJS operators. Handle sequential requests, priorities. Consider error handling, cancellation. Important for dependent operations.

Testing practices: unit tests for services, mock interceptors, integration tests. Consider error scenarios, async testing. Important for reliability, maintenance.

Documentation through Swagger/OpenAPI, custom documentation. Generate TypeScript interfaces, API services. Consider versioning, maintenance. Important for development workflow.