Middleware ordering in NestJS - Performance & Optimization

Performance: Middleware ordering

MEDIUM IMPACT

Middleware order affects how fast requests are processed and how many times the browser waits before getting a response.

Handling HTTP requests with multiple middleware functions

NestJS

app.use(lightMiddleware);
app.use(heavyMiddleware);

Light middleware runs first, quickly handling simple tasks and reducing delay before heavy processing.

📈 Performance GainReduces average request processing time, improving input responsiveness (INP).

Handling HTTP requests with multiple middleware functions

NestJS

app.use(heavyMiddleware);
app.use(lightMiddleware);

Heavy middleware runs before lightweight ones, causing unnecessary delay for all requests.

📉 Performance CostBlocks request processing longer, increasing input delay (INP) for users.

Performance Comparison

Pattern	Middleware Order	Request Delay	User Impact	Verdict
Heavy middleware first	Heavy → Light	High delay	Slower response, worse INP	[X] Bad
Light middleware first	Light → Heavy	Lower delay	Faster response, better INP	[OK] Good

Rendering Pipeline

Middleware runs on the server before sending a response. The order affects how quickly the server can start sending data back to the browser.

→Request Handling

→Response Preparation

⚠️ BottleneckRequest Handling stage due to synchronous or heavy middleware blocking the pipeline.

Core Web Vital Affected

INP

Middleware order affects how fast requests are processed and how many times the browser waits before getting a response.

Optimization Tips

1Place lightweight middleware before heavy middleware to reduce request delay.

2Avoid blocking operations early in middleware to improve input responsiveness (INP).

3Use asynchronous middleware wisely to prevent blocking the request pipeline.

Performance Quiz - 3 Questions

Why should lightweight middleware run before heavy middleware in NestJS?

A To delay response so the server can prepare more data

B To reduce request processing time and improve input responsiveness

C To increase bundle size for better caching

D To avoid using asynchronous code

DevTools: Network and Performance panels

How to check: Record a performance profile while making requests; check waterfall timings and server response times.

What to look for: Look for long server processing times before response starts, indicating middleware blocking.