NestJS vs Express vs Fastify comparison - Visual Side-by-Side Comparison

Concept Flow - NestJS vs Express vs Fastify comparison

Start Request

↓

NestJS Middleware

↓

NestJS Controller

↓

Underlying HTTP Framework

↓

Express

↓

Handle Request & Response

↓

Send Response

↓

End

Shows how NestJS handles requests by using middleware and controllers, then delegates to an underlying HTTP framework like Express or Fastify to process and respond.

Execution Sample

NestJS

import { Controller, Get } from '@nestjs/common';
@Controller('hello')
export class HelloController {
  @Get()
  getHello() { return 'Hello World'; }
}

A simple NestJS controller that responds with 'Hello World' when a GET request is made to /hello.

Execution Table

Step	Action	NestJS Layer	Underlying Framework	Result
1	Receive HTTP GET /hello	Middleware processes request	Express or Fastify receives request	Request passed to controller
2	Controller method getHello() called	Controller handles route	Underlying framework idle	Returns 'Hello World' string
3	NestJS sends response	Response prepared	Underlying framework sends HTTP response	Client receives 'Hello World'
4	Request cycle ends	Cleanup if needed	Request closed	Ready for next request

💡 Request handled fully by NestJS and underlying framework sends response back to client

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
request	undefined	HTTP GET /hello object	Passed to controller	Response prepared	Request closed
response	undefined	undefined	undefined	'Hello World' string	Sent to client

Key Moments - 2 Insights

Why does NestJS use Express or Fastify under the hood?

NestJS is a framework that builds on top of existing HTTP servers like Express or Fastify to add structure and features. The execution_table shows NestJS middleware and controllers handle logic, but the underlying framework manages the actual HTTP request and response.

How does Fastify differ from Express in this setup?

Fastify is designed for speed and low overhead, so when NestJS uses Fastify (seen in the underlying framework column), requests may be processed faster compared to Express. The flow is similar but performance differs.

Visual Quiz - 3 Questions

Look at the execution_table, what happens at Step 2?

A NestJS controller method is called to handle the route

B Underlying framework sends the HTTP response

C Request is received by the server

D Request cycle ends and cleanup happens

💡 Hint

Check the 'Action' and 'NestJS Layer' columns at Step 2 in the execution_table

At which step does the client receive the 'Hello World' response?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for when the response is sent to the client in the 'Result' column

If NestJS used only Express, which column in the execution_table would change?

A NestJS Layer

B Underlying Framework

C Action

D Result

💡 Hint

The 'Underlying Framework' column shows which HTTP server is used

Concept Snapshot

NestJS is a framework that uses Express or Fastify underneath.
It adds structure with controllers and middleware.
Express is popular and easy; Fastify is faster and lighter.
NestJS handles routing and logic; Express/Fastify handle HTTP.
Choose Fastify for speed, Express for ecosystem.
NestJS lets you switch easily between them.

Full Transcript

This visual execution compares NestJS with Express and Fastify. NestJS acts as a structured layer on top of HTTP servers like Express or Fastify. When a request comes in, NestJS middleware processes it, then the controller handles the route logic. The underlying framework (Express or Fastify) manages the actual HTTP request and response. Express is widely used and easy to work with, while Fastify offers better performance. The execution table shows the step-by-step flow: receiving the request, calling the controller, preparing the response, and sending it back to the client. Variables like request and response change state through these steps. Key points include understanding NestJS's role as a wrapper and the performance differences between Express and Fastify. The quiz tests understanding of these steps and roles. Overall, NestJS provides a clean structure while leveraging powerful HTTP frameworks underneath.