Global middleware in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to apply a middleware globally in a NestJS app.

NestJS

app.[1](new LoggerMiddleware());

Drag options to blanks, or click blank then click option'

Aapply

Buse

Cregister

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'apply' or 'register' instead of 'use' causes errors.

Trying to call middleware without the 'new' keyword.

In NestJS, to apply middleware globally, you use the app.use() method.

2fill in blank

medium

Complete the code to implement a middleware class with the correct method signature.

NestJS

export class LoggerMiddleware implements NestMiddleware {
  [1](req: Request, res: Response, next: Function) {
    console.log('Request logged');
    next();
  }
}

Drag options to blanks, or click blank then click option'

Ause

Brun

Capply

Dhandle

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'handle' or 'apply' instead of 'use' causes NestJS to not recognize the middleware.

Missing the 'next()' call inside the method.

The middleware class must implement a use method to handle requests.

3fill in blank

medium

Complete the code to apply the middleware globally in the bootstrap function.

NestJS

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.[1](new LoggerMiddleware());
  await app.listen(3000);
}

Drag options to blanks, or click blank then click option'

Aregister

Bapply

Cuse

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'apply' which is used in module configuration.

Forgetting the 'new' keyword (though shown here).

In NestJS, to apply middleware globally, you use the app.use(new LoggerMiddleware()) method on the app instance.

4fill in blank

hard

Fill both blanks to correctly configure global middleware in the main module.

NestJS

import { MiddlewareConsumer, Module, [1] } from '@nestjs/common';

@Module({})
export class AppModule implements [2] {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(LoggerMiddleware).forRoutes('*');
  }
}

Drag options to blanks, or click blank then click option'

ANestModule

BNestMiddleware

CMiddlewareModule

DMiddlewareHandler

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'NestMiddleware' instead of 'NestModule' for the module class.

Not importing the interface before implementing it.

The module must implement NestModule to configure middleware.

5fill in blank

hard

Fill all three blanks to create a middleware that logs request method and URL.

NestJS

export class LoggerMiddleware implements NestMiddleware {
  use(req: Request, res: Response, [1]) {
    console.log(`${req.[2] request to ${req.[3]`);
    next();
  }
}

Drag options to blanks, or click blank then click option'

Anext

Bmethod

Curl

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to call next() causes the request to hang.

Using incorrect property names like 'request' instead of 'method' or 'url'.

The middleware method receives next as the third argument. The request method is req.method and the URL is req.url.

Practice

1. What is the main purpose of global middleware in a NestJS application?

easy

A. To define database models for the application

B. To run code on every incoming request before reaching route handlers

C. To create new routes dynamically

D. To handle errors after the response is sent

Solution

1. Step 1: Understand middleware role

   Middleware runs before route handlers to process requests or add features like logging.

2. Step 2: Identify global middleware scope

   Global middleware runs on every request, so it applies common logic everywhere.

3. Final Answer:

   To run code on every incoming request before reaching route handlers -> Option B

4. Quick Check:

   Global middleware = runs on every request [OK]

Hint: Global middleware runs before routes on all requests [OK]

Common Mistakes:

• Confusing middleware with route handlers
• Thinking middleware only runs on some routes
• Mixing middleware with error handling

2. Which of the following is the correct way to apply a middleware globally in NestJS?

easy

A. app.useGlobalMiddleware(MyMiddleware)

B. consumer.apply(MyMiddleware).forRoutes('users')

C. consumer.apply(MyMiddleware).forRoutes('*')

D. app.applyMiddlewareGlobally(MyMiddleware)

Solution

1. Step 1: Recall global middleware syntax

   In NestJS, the recommended way to apply middleware globally is using app.useGlobalMiddleware(MyMiddleware).

2. Step 2: Compare options

   consumer.apply(MyMiddleware).forRoutes('*') applies middleware to all routes but is not truly global middleware; app.useGlobalMiddleware applies middleware globally.

3. Final Answer:

   app.useGlobalMiddleware(MyMiddleware) -> Option A

4. Quick Check:

   Global middleware uses app.useGlobalMiddleware [OK]

Hint: Use app.useGlobalMiddleware to apply middleware globally [OK]

Common Mistakes:

• Using consumer.apply(...).forRoutes('*') for global middleware
• Trying to call non-existent app methods
• Confusing middleware registration with guards

3. Given this middleware code, what will be logged for every request?

export class LoggerMiddleware implements NestMiddleware {
  use(req: Request, res: Response, next: Function) {
    console.log(`Request to: ${req.url}`);
    next();
  }
}

// Applied globally with consumer.apply(LoggerMiddleware).forRoutes('*')

medium

A. Logs the HTTP method only

B. Logs the response status code

C. Logs nothing because next() is missing

D. Logs the URL of every incoming request

Solution

1. Step 1: Analyze middleware code

   The middleware logs the string 'Request to:' plus the request URL from req.url.

2. Step 2: Understand global application

   Since applied globally, this log happens on every request URL received by the app.

3. Final Answer:

   Logs the URL of every incoming request -> Option D

4. Quick Check:

   LoggerMiddleware logs req.url every request [OK]

Hint: Look for console.log inside middleware use() method [OK]

Common Mistakes:

• Assuming HTTP method is logged instead of URL
• Forgetting next() causes no further processing
• Thinking response status is logged

4. Identify the error in this global middleware setup:

export class AuthMiddleware implements NestMiddleware {
  use(req: Request, res: Response) {
    if (!req.headers.authorization) {
      res.status(401).send('Unauthorized');
    }
  }
}

// Applied with consumer.apply(AuthMiddleware).forRoutes('*')

medium

A. Missing call to next() to continue request processing

B. Middleware should not check headers

C. forRoutes('*') cannot be used for global middleware

D. res.status(401) is invalid syntax

Solution

1. Step 1: Check middleware method signature

   The use method lacks the next parameter and does not call next(), so request stops here.

2. Step 2: Understand middleware flow

   Without calling next(), the request will hang or not proceed to route handlers after middleware.

3. Final Answer:

   Missing call to next() to continue request processing -> Option A

4. Quick Check:

   Middleware must call next() to proceed [OK]

Hint: Always call next() in middleware to continue [OK]

Common Mistakes:

• Omitting next() call in middleware
• Misunderstanding middleware flow control
• Thinking forRoutes('*') is invalid

5. You want to apply a logging middleware globally but only for HTTP POST requests. Which approach correctly achieves this in NestJS?

hard

A. Use consumer.apply(LoggerMiddleware).forRoutes('*') and check req.method inside middleware

B. Apply middleware only on POST routes manually, no global option

C. Use consumer.apply(LoggerMiddleware).forRoutes({ path: '*', method: RequestMethod.POST })

D. Use app.useGlobalMiddleware(LoggerMiddleware) with method filter

Solution

1. Step 1: Understand route filtering in middleware

   NestJS allows filtering middleware by path and HTTP method using forRoutes with an object.

2. Step 2: Apply middleware globally but only for POST

   Using forRoutes({ path: '*', method: RequestMethod.POST }) applies middleware to all paths but only POST requests.

3. Step 3: Evaluate other options

   Use consumer.apply(LoggerMiddleware).forRoutes('*') and check req.method inside middleware applies middleware on all methods, not just POST. Apply middleware only on POST routes manually, no global option is manual, not global. Use app.useGlobalMiddleware(LoggerMiddleware) with method filter is invalid syntax.

4. Final Answer:

   Use consumer.apply(LoggerMiddleware).forRoutes({ path: '*', method: RequestMethod.POST }) -> Option C

5. Quick Check:

   forRoutes with method filter = selective global middleware [OK]

Hint: Use forRoutes({ path: '*', method: RequestMethod.POST }) for selective global [OK]

Common Mistakes:

• Applying middleware globally without method filter
• Trying non-existent app.useGlobalMiddleware method
• Manually applying middleware on each POST route