NestJS vs Express vs Fastify comparison - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Which framework uses a modular architecture with decorators?

Among NestJS, Express, and Fastify, which framework is designed around a modular architecture using decorators to organize code?

A Express

B NestJS

C Fastify

D All three use decorators by default

💡 Hint

Think about which framework uses TypeScript features heavily.

NestJS uses decorators and a modular structure to organize code, making it more structured and scalable.

❓ component_behavior

intermediate

What is the default HTTP server used by NestJS?

By default, which HTTP server does NestJS use under the hood?

A Fastify

B Koa

C Express

D Hapi

💡 Hint

NestJS can switch servers but has a default choice.

NestJS uses Express as its default HTTP server but can be configured to use Fastify for better performance.

📝 Syntax

advanced

Which code snippet correctly creates a Fastify instance in NestJS?

Select the correct way to create a Fastify-based NestJS application.

NestJS

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { FastifyAdapter, NestFastifyApplication } from '@nestjs/platform-fastify';

async function bootstrap() {
  const app = await NestFactory.create(AppModule, new FastifyAdapter());
  await app.listen(3000);
}
bootstrap();

A NestFactory.create(AppModule, new KoaAdapter())

B NestFactory.create(AppModule, new ExpressAdapter())

C NestFactory.create(AppModule)

D NestFactory.create(AppModule, new FastifyAdapter())

💡 Hint

Fastify requires a specific adapter in NestJS.

To use Fastify in NestJS, you must pass a FastifyAdapter instance to NestFactory.create.

❓ state_output

advanced

What is the output when sending a GET request to a simple Express route?

Given this Express code, what will the server respond with when a GET request is made to '/'? const express = require('express'); const app = express(); app.get('/', (req, res) => { res.send('Hello from Express'); }); app.listen(3000);

A Hello from Express

B Cannot GET /

C Hello from NestJS

D 404 Not Found

💡 Hint

Look at the response sent inside the route handler.

The Express app sends 'Hello from Express' as the response to GET requests at '/'.

❓ lifecycle

expert

Which lifecycle hook runs after all modules are initialized in NestJS?

In NestJS, which lifecycle hook method is called after all modules have been initialized?

A onApplicationBootstrap()

B onModuleInit()

C afterInit()

D beforeApplicationShutdown()

💡 Hint

This hook runs once the whole app is ready, not just a single module.

onApplicationBootstrap() is called after all modules are initialized and the app is bootstrapped.

Practice

1. Which framework is known for providing a structured architecture with decorators and dependency injection?

easy

A. Fastify

B. Express

C. NestJS

D. Koa

Solution

1. Step 1: Understand framework features

   NestJS is designed with a modular architecture, using decorators and dependency injection to organize code clearly.

2. Step 2: Compare with other frameworks

   Express is minimal and flexible but lacks built-in structure; Fastify focuses on speed but not on architectural patterns.

3. Final Answer:

   NestJS -> Option C

4. Quick Check:

   Structured framework = NestJS [OK]

Hint: Structured + decorators = NestJS [OK]

Common Mistakes:

• Confusing Express's flexibility with structure
• Thinking Fastify has built-in dependency injection
• Choosing Koa which is unrelated here

2. Which of the following is the correct way to create a Fastify server instance?

easy

A. const app = fastify();

B. const app = express();

C. const app = new NestFactory();

D. const app = new Koa();

Solution

1. Step 1: Recall Fastify server creation syntax

   Fastify servers are created by calling the fastify() function, not using new keyword.

2. Step 2: Eliminate other options

   Express uses express(), NestJS uses NestFactory.create(), and Koa uses new Koa().

3. Final Answer:

   const app = fastify(); -> Option A

4. Quick Check:

   Fastify instance = fastify() [OK]

Hint: Fastify uses fastify() function call [OK]

Common Mistakes:

• Using new keyword with fastify
• Confusing Express and Fastify syntax
• Using NestFactory directly for Fastify

3. Given the following code snippet, what will be the main difference in performance between NestJS using Express and Fastify?

const app = await NestFactory.create(AppModule, { logger: true });
await app.listen(3000);

medium

A. NestJS with Express is faster due to simpler middleware

B. NestJS with Fastify is faster due to optimized HTTP handling

C. Both have identical performance because NestJS abstracts the server

D. NestJS with Express supports HTTP/2 by default, Fastify does not

Solution

1. Step 1: Understand NestJS adapters

   NestJS can use Express or Fastify under the hood. Fastify is designed for speed and efficiency.

2. Step 2: Compare performance traits

   Fastify has optimized HTTP handling and lower overhead, making it faster than Express in most cases.

3. Final Answer:

   NestJS with Fastify is faster due to optimized HTTP handling -> Option B

4. Quick Check:

   Fastify = faster HTTP handling [OK]

Hint: Fastify is faster than Express in NestJS [OK]

Common Mistakes:

• Assuming Express is faster due to simplicity
• Thinking NestJS removes all performance differences
• Confusing HTTP/2 support defaults

4. You wrote a NestJS app using Fastify adapter but get an error: TypeError: app.listen is not a function. What is the most likely cause?

medium

A. You forgot to import FastifyModule in AppModule

B. Fastify does not support listen method

C. You called app.listen before await

D. You did not use NestFactory.create with Fastify adapter

Solution

1. Step 1: Check how NestJS app is created with Fastify

   To use Fastify, you must pass the Fastify adapter to NestFactory.create().

2. Step 2: Understand error cause

   If you skip the adapter, NestJS defaults to Express, but if you mix Fastify code without adapter, app.listen may be undefined.

3. Final Answer:

   You did not use NestFactory.create with Fastify adapter -> Option D

4. Quick Check:

   Fastify adapter required for app.listen [OK]

Hint: Use Fastify adapter in NestFactory.create [OK]

Common Mistakes:

• Assuming FastifyModule import is enough
• Calling listen without await causes different error
• Thinking Fastify lacks listen method

5. You want to build a high-performance REST API with automatic validation, modular structure, and fast response times. Which combination best fits this requirement?

hard

A. NestJS using Fastify adapter with class-validator and modules

B. Fastify with no framework on top

C. NestJS using Express adapter without validation

D. Express with manual middleware and no structure

Solution

1. Step 1: Identify requirements

   High performance, automatic validation, and modular structure require a framework with features and speed.

2. Step 2: Match frameworks to needs

   Express alone lacks structure and automatic validation; Fastify alone lacks modularity; NestJS provides structure and validation, and Fastify adapter adds speed.

3. Final Answer:

   NestJS using Fastify adapter with class-validator and modules -> Option A

4. Quick Check:

   Structure + validation + speed = NestJS + Fastify [OK]

Hint: Combine NestJS structure + Fastify speed + validation [OK]

Common Mistakes:

• Choosing Express for automatic validation
• Ignoring modularity in Fastify alone
• Using NestJS with Express loses speed advantage