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What is an HTTP interceptor?

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01

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Explain interceptors and use cases.

httpinterceptor
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An interceptor implements HttpInterceptor and sits in the HttpClient pipeline, letting you transform every outgoing request or incoming response — e.g. attach auth tokens, add headers, log, retry, or handle errors globally — without touching each call site.

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A functional auth interceptor
import { HttpInterceptorFn } from '@angular/common/http';

export const authInterceptor: HttpInterceptorFn = (req, next) => {
  const token = localStorage.getItem('token');
  // requests are immutable → clone with the extra header
  const authReq = token
    ? req.clone({ setHeaders: { Authorization: 'Bearer ' + token } })
    : req;
  return next(authReq);
};

// register:  provideHttpClient(withInterceptors([authInterceptor]))
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