Applying middleware to routes in NestJS - Performance & Optimization

Performance: Applying middleware to routes

MEDIUM IMPACT

Middleware affects the request processing speed and can impact the time before the route handler executes, influencing interaction responsiveness.

Applying middleware to all routes indiscriminately

NestJS

app.use('/api/users', userMiddleware); // applies middleware only to /api/users routes

Middleware runs only on targeted routes, reducing unnecessary processing and improving responsiveness.

📈 Performance Gainreduces middleware executions, lowering INP latency

Applying middleware to all routes indiscriminately

NestJS

app.use(globalMiddleware); // applies middleware to every route

Middleware runs on every request, even when not needed, causing unnecessary processing and slower response times.

📉 Performance Costadds processing overhead on every request, increasing INP latency

Performance Comparison

Pattern	Middleware Runs	Processing Overhead	Response Delay	Verdict
Global middleware on all routes	Every request	High	Increased INP latency	[X] Bad
Middleware applied to specific routes	Only targeted requests	Low	Minimal delay	[OK] Good

Rendering Pipeline

Middleware runs during the server request lifecycle before the route handler, affecting how fast the server can respond to user input.

→Request Processing

→Route Matching

→Handler Execution

⚠️ BottleneckMiddleware processing time before route handler

Core Web Vital Affected

INP

Middleware affects the request processing speed and can impact the time before the route handler executes, influencing interaction responsiveness.

Optimization Tips

1Apply middleware only to routes that require it to reduce processing overhead.

2Keep middleware logic lightweight to minimize request handling delay.

3Avoid global middleware unless absolutely necessary to improve input responsiveness.

Performance Quiz - 3 Questions

What is the main performance risk of applying middleware globally to all routes in NestJS?

A Middleware runs on every request, causing unnecessary processing.

B Middleware reduces bundle size.

C Middleware improves LCP by preloading data.

D Middleware eliminates layout shifts.

DevTools: Network

How to check: Open DevTools Network panel, filter requests by route, and compare response times with and without middleware.

What to look for: Look for increased response time on routes with middleware indicating processing overhead.

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