Angular Interceptors: API & Error Optimization

Introduction:

Angular interceptors are powerful tools for managing HTTP requests and responses. They provide a way to intercept and modify HTTP traffic globally in an Angular application. Whether you need to add headers to requests, handle errors, or log responses, interceptors have got you covered. This comprehensive guide will systematically explore Angular interceptors with easy-to-understand examples.

Understanding Interceptors:

Angular interceptors act as middleware for HTTP requests and responses. They sit between your application and the Angular HttpClient, allowing you to intercept and transform HTTP traffic.

Setting Up Your Interceptors:

To create an interceptor, start by generating a new Angular service:

ng generate service interceptors/http

Implementing the Interceptor:

Open the generated service file (http.interceptor.ts) and import the necessary modules:

import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent, HttpResponse } from '@angular/common/http';
import { Observable } from 'rxjs';
import { tap } from 'rxjs/operators';

Creating the Interceptor Class:

Implement the HttpInterceptor Interface in your service class:

@Injectable()
export class HttpInterceptorService implements HttpInterceptor {
constructor() {}

intercept(request: HttpRequest, next: HttpHandler): Observable> {
// Your interceptor logic goes here
}
}  

Handling Requests:

Inside the intercept Method: you can modify the outgoing request before it’s sent:

intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
  // Clone the request and add headers
  const modifiedRequest = request.clone({
    setHeaders: {
      Authorization: 'Bearer token123'
    }
  });
  // Pass the modified request to the next handler
  return next.handle(modifiedRequest);
}

Handling Responses:

You can also intercept and modify incoming responses:

intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
  return next.handle(request).pipe(
    tap((event: HttpEvent<any>) => {
      if (event instanceof HttpResponse) {
        // Log the response
        console.log('Response:', event);
      }
    })
  );
}

Registering Interceptors:

Finally, register your interceptor in the app module:

providers: [
  { provide: HTTP_INTERCEPTORS, useClass: HttpInterceptorService, multi: true }
]

Conclusion:

Angular interceptors are invaluable tools for managing HTTP traffic in your application. Interceptors offer a flexible and efficient solution whether you need to modify requests, handle responses, or implement custom logic. By following this comprehensive guide, you’ll be able to harness the full power of interceptors to enhance the functionality and reliability of your Angular applications.

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