Interceptor in Angular

In Angular, an interceptor is a way to intercept HTTP requests or responses before they are sent or received by the application. Interceptors allow you to modify the request or response, add custom headers, handle errors, or perform any other operations that are necessary for every HTTP call.

To create an interceptor in Angular, you typically follow these steps:

Create the Interceptor Class:

1. Create a new Angular service:

                   
                       ng generate service interceptor
                   
               

2. Implement the interceptor:

   In the generated service file (interceptor.service.ts), implement the HttpInterceptor interface and define the intercept method. This method intercepts HTTP requests and responses.

                   
                       import { Injectable } from '@angular/core';
                       import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from '@angular/common/http';
                       import { Observable } from 'rxjs';
                       
                       @Injectable()
                       export class MyInterceptor implements HttpInterceptor {
                         intercept(req: HttpRequest, next: HttpHandler): Observable> {
                           // Modify or handle the request here
                           // For example, adding headers
                           const modifiedReq = req.clone({
                             setHeaders: {
                               'Authorization': 'Bearer ',
                               'Content-Type': 'application/json'
                             }
                           });
                           
                           // Pass the modified request to the next handler
                           return next.handle(modifiedReq);
                         }
                       }                    
                   
               

Register the Interceptor

1. Provide the interceptor:

   In your Angular module (often app.module.ts), you need to provide the interceptor by adding it to the providers array and importing necessary modules.

                   
                       import { NgModule } from '@angular/core';
                       import { BrowserModule } from '@angular/platform-browser';
                       import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';
                       import { MyInterceptor } from './interceptor.service';
                       
                       @NgModule({
                         imports: [BrowserModule, HttpClientModule],
                         providers: [
                           {
                             provide: HTTP_INTERCEPTORS,
                             useClass: MyInterceptor,
                             multi: true
                           }
                         ],
                         bootstrap: [AppComponent]
                       })
                       export class AppModule { }                    
                   
               

Notes:

• The HTTP_INTERCEPTORS token is used to provide a list of interceptors.
• Using multi: true allows multiple interceptors to be registered in the application.
• Interceptors are often used for tasks like authentication, error handling, logging, etc.

Remember to adjust the interceptor's logic to suit your application's requirements.

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