NodeJS
How to create Intercepter in nestjs
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Introduction
In NestJS, interceptors serve functions such as modifying the incoming request, the outgoing response, logging, transformations, and caching. They share a lot of characteristics with middleware, although they are much more exact, such as transforming responses or adding more functionality.
Follow these instructions to make and implement interceptors in NestJS:
Step 1: Create an Interceptor
You may create the file directly or use the NestJS CLI to create the interceptor.
Type the following command into the CLI:
nest g interceptor loggingA new file called logging.interceptor.ts will now be generated.
Step 2: Implement the Interceptor Logic
For interceptors to work, interceptors need to implement the NestInterceptor interface that has an intercept() method. This method comes with two parameters: the context of the execution and a handler which lets one pass the request to the next function in the lifecycle.
Here is all the code for the logging interceptor, which logs the request and the response:
import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';import { Observable } from 'rxjs';import { tap } from 'rxjs/operators';@Injectable()export class LoggingInterceptor implements NestInterceptor { intercept(context: ExecutionContext, next: CallHandler): Observable<any> { const now = Date.now(); console.log('Before the handler...'); return next .handle() .pipe( tap(() => console.log(`After the handler... ${Date.now() - now}ms`)), ); }}
In this case, the intercept method measures time, and can therefore be used for performance monitoring.
Step 3: Apply the Interceptor
An interceptor can be applied at the method level, the controller level, or globally.
Globally: In main.ts:
import { LoggingInterceptor } from './logging.interceptor';import { AppModule } from './app.module';async function bootstrap() { const app = await NestFactory.create(AppModule); app.useGlobalInterceptors(new LoggingInterceptor()); await app.listen(3000);}bootstrap();
Controller Level: For all methods within a controller, you set the interceptor.
import { Controller, UseInterceptors, Get } from '@nestjs/common';import { LoggingInterceptor } from './logging.interceptor';@Controller('example')@UseInterceptors(LoggingInterceptor)export class ExampleController { @Get() getExample() { return 'This is an example'; }}
Method Level: Applying the interceptor to a particular route.
@Get('example')@UseInterceptors(LoggingInterceptor)getExample() { return 'This is an example';}
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