Applying middleware to routes in NestJS - Mini Project: Build & Apply

Applying middleware to routes in NestJS

📖 Scenario: You are building a simple NestJS server that logs requests to certain routes. Middleware helps you run code before the route handler runs, like logging or checking permissions.

🎯 Goal: Create a NestJS middleware that logs a message for requests, then apply it only to the /cats route.

📋 What You'll Learn

Create a middleware class called LoggerMiddleware that logs 'Request received' when a request comes in.

Create a controller called CatsController with a GET route at /cats that returns a simple string.

Apply the LoggerMiddleware only to the /cats route using the configure method in the main module.

Ensure the middleware runs before the route handler and logs the message.

💡 Why This Matters

🌍 Real World

Middleware is used in real web servers to add logging, security checks, or modify requests before they reach the main route handlers.

💼 Career

Understanding middleware application is essential for backend developers working with NestJS or similar frameworks to build scalable and maintainable server applications.

1

Create the LoggerMiddleware class

Create a class called LoggerMiddleware that implements NestMiddleware. Inside the use method, log the string 'Request received' and call next().

NestJS

import { Injectable, NestMiddleware } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';

@Injectable()
export class LoggerMiddleware implements NestMiddleware {
  use(req: Request, res: Response, next: NextFunction) {
    // Your code here
  }
}

Need a hint?

Remember to import NestMiddleware and implement the use method with req, res, and next parameters.

2

Create the CatsController with a GET /cats route

Create a controller class called CatsController with a @Controller('cats') decorator. Add a GET route method called findAll that returns the string 'This action returns all cats'.

NestJS

import { Controller, Get } from '@nestjs/common';

@Controller('cats')
export class CatsController {
  // Your code here
}

Need a hint?

Use the @Controller('cats') decorator and add a method with @Get() that returns the required string.

3

Apply LoggerMiddleware only to the /cats route

In the main module class called AppModule, implement the configure method. Use consumer.apply(LoggerMiddleware).forRoutes('cats') to apply the middleware only to the /cats route.

NestJS

import { Module, MiddlewareConsumer, NestModule } from '@nestjs/common';

@Module({
  controllers: [CatsController],
  providers: [],
})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    // Your code here
  }
}

Need a hint?

Implement NestModule and use the configure method to apply middleware to the 'cats' route.

4

Complete the module with imports and exports

Add the LoggerMiddleware to the providers array in @Module so NestJS can inject it properly.

NestJS

import { Injectable, NestMiddleware, Module, MiddlewareConsumer, NestModule } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';
import { Controller, Get } from '@nestjs/common';

@Injectable()
export class LoggerMiddleware implements NestMiddleware {
  use(req: Request, res: Response, next: NextFunction) {
    console.log('Request received');
    next();
  }
}

@Controller('cats')
export class CatsController {
  @Get()
  findAll(): string {
    return 'This action returns all cats';
  }
}

@Module({
  controllers: [CatsController],
  providers: [
    // Add LoggerMiddleware here
  ],
})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(LoggerMiddleware).forRoutes('cats');
  }
}

Need a hint?

Add LoggerMiddleware to the providers array inside the @Module decorator.