Applying middleware to routes in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to apply middleware to all routes in a NestJS module.

NestJS

import { MiddlewareConsumer, Module, NestModule } from '@nestjs/common';
import { LoggerMiddleware } from './logger.middleware';

@Module({})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(LoggerMiddleware).[1]('*');
  }
}

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

Aattach

Buse

CapplyToRoutes

DforRoutes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'use' instead of 'forRoutes' causes a syntax error.

Trying to call 'applyToRoutes' which does not exist.

In NestJS, to apply middleware to routes, you use the 'forRoutes' method on the MiddlewareConsumer.

2fill in blank

medium

Complete the code to apply middleware only to the 'users' route.

NestJS

consumer.apply(LoggerMiddleware).forRoutes({ path: '[1]', method: RequestMethod.ALL });

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

Ausers

Bproducts

Corders

Dauth

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong route path string causes middleware not to apply.

Forgetting to import RequestMethod when specifying method.

To apply middleware to a specific route, specify the route path string in the 'forRoutes' method.

3fill in blank

hard

Fix the error in the code to apply middleware to multiple routes.

NestJS

consumer.apply(LoggerMiddleware).forRoutes({ path: 'users', method: RequestMethod.GET }, [1]);

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

A'orders'

B['orders', 'products']

C{ path: 'orders', method: RequestMethod.POST }

DRequestMethod.POST

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an array of strings instead of route objects causes errors.

Passing only method without path is invalid.

To apply middleware to multiple routes, pass multiple route objects to 'forRoutes'.

4fill in blank

hard

Fill both blanks to apply middleware only to POST and PUT methods on 'products' route.

NestJS

consumer.apply(LoggerMiddleware).forRoutes({ path: 'products', method: [1] }, { path: 'products', method: [2] });

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

ARequestMethod.POST

BRequestMethod.GET

CRequestMethod.PUT

DRequestMethod.DELETE

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET or DELETE instead of POST or PUT.

Passing strings instead of RequestMethod enum values.

To target POST and PUT methods, use RequestMethod.POST and RequestMethod.PUT respectively.

5fill in blank

hard

Fill all three blanks to apply middleware to 'auth' route for GET, POST, and DELETE methods.

NestJS

consumer.apply(AuthMiddleware).forRoutes(
  { path: 'auth', method: [1] },
  { path: 'auth', method: [2] },
  { path: 'auth', method: [3] }
);

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

ARequestMethod.GET

BRequestMethod.POST

CRequestMethod.DELETE

DRequestMethod.PUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using PUT instead of DELETE.

Passing strings instead of RequestMethod enum values.

Middleware can be applied to multiple HTTP methods by passing route objects with different methods.

Practice

1. What is the main purpose of applying middleware to routes in a NestJS application?

easy

A. To run code before the route handler processes the request

B. To directly send responses without reaching the route handler

C. To replace the route handler with a new function

D. To automatically generate API documentation

Solution

1. Step 1: Understand middleware role

   Middleware runs before the route handler to process or modify requests.

2. Step 2: Identify middleware effect on routes

   It does not replace handlers or generate docs but can log or check requests first.

3. Final Answer:

   To run code before the route handler processes the request -> Option A

4. Quick Check:

   Middleware runs before route handlers [OK]

Hint: Middleware always runs before route handlers [OK]

Common Mistakes:

• Thinking middleware replaces route handlers
• Confusing middleware with response sending
• Assuming middleware auto-generates docs

2. Which of the following is the correct syntax to apply a middleware named LoggerMiddleware to all routes in a NestJS module?

easy

A. consumer.use(LoggerMiddleware).forRoutes('/');

B. consumer.apply(LoggerMiddleware).forRoutes('/');

C. consumer.apply(LoggerMiddleware).forRoutes('*');

D. consumer.apply(LoggerMiddleware).toRoutes('*');

Solution

1. Step 1: Recall NestJS middleware syntax

   The correct method to apply middleware is consumer.apply(...).forRoutes(...).

2. Step 2: Identify correct route pattern for all routes

   Using '/' applies middleware to all routes; '*' is invalid.

3. Final Answer:

   consumer.apply(LoggerMiddleware).forRoutes('/'); -> Option B

4. Quick Check:

   Use apply + forRoutes('/') for all routes [OK]

Hint: Use apply() with forRoutes('/') to cover all routes [OK]

Common Mistakes:

• Using use() instead of apply()
• Using toRoutes() which is invalid
• Using '*' instead of '/' for all routes

3. Given this middleware application code in a NestJS module:

consumer.apply(AuthMiddleware).forRoutes('users');

Which routes will have the AuthMiddleware applied?

medium

A. All routes including '/users' and '/users/:id'

B. Only routes with path exactly '/users'

C. All routes in the application

D. No routes, because the path is invalid

Solution

1. Step 1: Understand forRoutes string behavior

   Passing 'users' applies middleware to all routes starting with '/users', including parameters.

2. Step 2: Confirm middleware coverage

   This includes '/users', '/users/123', '/users/profile', etc., not the entire app.

3. Final Answer:

   All routes including '/users' and '/users/:id' -> Option A

4. Quick Check:

   forRoutes('users') covers prefix routes [OK]

Hint: forRoutes('path') applies middleware to that path and subpaths [OK]

Common Mistakes:

• Thinking only exact path matches get middleware
• Assuming middleware applies globally without '*'
• Believing invalid path disables middleware

4. Examine this NestJS middleware setup:

export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(AuthMiddleware).forRoutes();
  }
}

What is the issue with this code?

medium

A. Middleware class must be decorated with @Injectable

B. Middleware is applied globally without specifying routes

C. Missing route argument in forRoutes causes a runtime error

D. MiddlewareConsumer is not imported correctly

Solution

1. Step 1: Check forRoutes usage

   The method forRoutes requires at least one argument specifying routes; empty call is invalid.

2. Step 2: Identify error type

   Calling forRoutes() without arguments causes a runtime error because no routes are defined.

3. Final Answer:

   Missing route argument in forRoutes causes a runtime error -> Option C

4. Quick Check:

   forRoutes() needs routes argument [OK]

Hint: Always provide routes to forRoutes() [OK]

Common Mistakes:

• Leaving forRoutes empty
• Assuming middleware applies globally without routes
• Ignoring missing @Injectable on middleware

5. You want to apply LoggerMiddleware only to POST requests on the /orders route in NestJS. Which approach correctly applies middleware only to POST /orders requests?

hard

A. Apply middleware globally and skip non-POST requests inside middleware

B. Use consumer.apply(LoggerMiddleware).forRoutes('orders'); and check method inside middleware

C. Use consumer.apply(LoggerMiddleware).forRoutes('orders'); without method filtering

D. Use consumer.apply(LoggerMiddleware).forRoutes({ path: 'orders', method: RequestMethod.POST });

Solution

1. Step 1: Understand method filtering in middleware

   NestJS allows specifying method with an object: { path, method } in forRoutes.

2. Step 2: Identify correct syntax for POST-only middleware

   Using consumer.apply(...).forRoutes({ path: 'orders', method: RequestMethod.POST }) applies middleware only to POST /orders.

3. Final Answer:

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

4. Quick Check:

   Use object with path and method in forRoutes for method filtering [OK]

Hint: Use forRoutes({path, method}) to target HTTP methods [OK]

Common Mistakes:

• Applying middleware to all methods without filtering
• Checking method inside middleware instead of in forRoutes
• Applying middleware globally and filtering inside middleware