Why controllers handle incoming requests in NestJS - Performance Evidence

Performance: Why controllers handle incoming requests

MEDIUM IMPACT

This affects how quickly the server processes and responds to user requests, impacting server response time and user experience.

Handling HTTP requests in a NestJS application

NestJS

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

@Controller('users')
export class UsersController {
  constructor(private readonly userService: UserService) {}

  @Get()
  async getUsers() {
    // Use async non-blocking operations
    const users = await this.userService.findAll();
    return users;
  }
}

Non-blocking async code allows server to handle other requests concurrently, reducing response delays.

📈 Performance GainImproves responsiveness, reduces server blocking, better INP scores

Handling HTTP requests in a NestJS application

NestJS

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

@Controller('users')
export class UsersController {
  @Get()
  async getUsers() {
    // Heavy synchronous processing here
    for (let i = 0; i < 1e8; i++) {}
    return { message: 'Users list' };
  }
}

Blocking synchronous code in controller delays response, increasing server response time and hurting user experience.

📉 Performance CostBlocks event loop, increasing response time by hundreds of milliseconds or more

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Blocking synchronous controller code	N/A (server-side)	N/A	N/A	[X] Bad
Asynchronous non-blocking controller code	N/A (server-side)	N/A	N/A	[OK] Good

Rendering Pipeline

Controllers receive incoming HTTP requests, process them (often asynchronously), and send responses. Efficient handling avoids blocking the event loop, allowing faster server responses.

→Request Handling

→Server Processing

→Response Sending

⚠️ BottleneckSynchronous/blocking code in controllers delays response and blocks event loop

Core Web Vital Affected

INP

This affects how quickly the server processes and responds to user requests, impacting server response time and user experience.

Optimization Tips

1Avoid blocking synchronous code inside controllers to keep server responsive.

2Use async/await or promises for non-blocking request handling.

3Monitor server response times to detect controller bottlenecks.

Performance Quiz - 3 Questions

What is the main performance risk of using synchronous code inside NestJS controllers?

A It causes layout shifts in the browser

B It blocks the event loop, delaying responses

C It increases CSS paint time

D It reduces bundle size

DevTools: Network panel in browser DevTools and server profiling tools

How to check: Open Network panel, observe server response times for requests handled by controllers; use server profiler to check event loop blocking

What to look for: Long server response times or blocked event loop indicate inefficient controller handling