The Ultimate Guide to Interceptors: Understanding Their Power and Functionality

An interceptor is a service that can intercept HTTP requests and responses. Interceptors provide a way to modify or handle requests and responses globally before they are sent to the server or returned to the client.

Interceptors are used for a variety of tasks such as:

1. Adding headers to requests or responses
2. Authentication and authorization of requests
3. Logging of requests and responses
4. Caching of requests
5. Error handling and retrying failed requests
6. Translating requests and responses to different formats
7. Transformation of request and response bodies.

Interceptors can be added to the HTTP pipeline by providing them as a provider in the app.module.ts file or at a component level using the provider's property.

Interceptors are implemented as classes that implement the HttpInterceptor interface. The HttpInterceptor interface has two methods:

1. intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> - This method intercepts the outgoing request and returns an Observable of HttpEvents.

2. handle(request: HttpRequest<any>): Observable<HttpEvent<any>> - This method handles the outgoing request and returns an Observable of HttpEvents.

The intercept method is called for each outgoing HTTP request and can modify the request or return the original request. The handle method is called for the last interceptor in the chain and is responsible for sending the request to the server.

By using interceptors, developers can write reusable code that can be used across multiple components and services.