Node.js + Express.js Cheat Sheet

PART 1 — Node.js Fundamentals

1. What Is Node.js?

Node.js lets you run JavaScript on the server instead of the browser.
It’s built for fast, scalable backend applications using non-blocking I/O.

2. Why Node.js?

Node.js is popular because:

Uses JavaScript everywhere
Handles many users efficiently
Huge npm ecosystem
Perfect for APIs and real-time apps

3. Installing Node

After installing Node:


node -v
npm -v

These commands verify Node and npm.

4. Running a File


node app.js

Executes your JavaScript file on the server.

5. Basic Node Program


console.log("Hello Node");

Node runs JavaScript line by line.

6. Modules

Node uses modules to organize code.

CommonJS Import


const fs = require("fs");

Export


module.exports = myFunc;

7. ES Modules

Modern syntax:


import fs from "fs";

Requires "type":"module" in package.json.

8. Built-in Modules

Common ones:


fs     → files  
path   → paths  
http   → server  
os     → system info

Used for core backend work.

9. File System (fs)

Read file:


fs.readFileSync("a.txt")

Write file:


fs.writeFileSync("a.txt","hi")

Used for file operations.

10. Path Module


path.join(__dirname,"file.txt")

Builds safe file paths.

11. Process Object


process.env.PORT

Access environment variables.

12. package.json

Project configuration file.

Contains:

dependencies
scripts
project metadata

13. npm

Node package manager.


npm install express

Downloads libraries.

14. nodemon

Auto-restarts server on code change.


npm i nodemon

Used during development.

PART 2 — Express.js Basics

15. What Is Express?

Express is a lightweight Node framework for building REST APIs and web servers.

It simplifies routing, middleware, and requests.

16. Installing Express


npm install express

Adds Express to project.

17. Basic Server


const express = require("express");
const app = express();

app.listen(3000);

Starts HTTP server.

18. Simple Route


app.get("/",(req,res)=>{
 res.send("Hello");
});

Responds to browser requests.

19. Request Object (req)

Contains client data:

params
query
body
headers

20. Response Object (res)

Used to send data back.


res.json()
res.status()
res.send()

21. HTTP Methods


GET    → read  
POST   → create  
PUT    → update  
DELETE → remove

Core REST operations.

22. JSON Middleware


app.use(express.json());

Allows reading JSON body.

Required for APIs.

PART 3 — Routing

23. Route Parameters


/users/:id

Access via:


req.params.id

Used for dynamic routes.

24. Query Parameters


/users?page=1

Access:


req.query.page

Used for filters.

25. Router


const router = express.Router();

Splits routes into files.

Improves structure.

26. Route Files


routes/
 controllers/

Professional project separation.

PART 4 — Middleware

27. What Is Middleware?

Middleware runs between request and response.

Used for:

auth
logging
validation

28. Custom Middleware


app.use((req,res,next)=>{
 next();
});

next() passes control.

29. Third-Party Middleware

Examples:


cors  
morgan  
helmet

Add security and logging.

30. Error Middleware


app.use((err,req,res,next)=>{})

Central error handling.

PART 5 — MVC Architecture

31. Model

Database logic.

32. Controller

Business logic.

33. Routes

URL definitions.

This separation keeps backend clean and scalable.

PART 6 — Database Integration

34. MongoDB + Mongoose

Popular NoSQL combo.


mongoose.connect()

35. Schema

Defines data structure.


new Schema({})

36. Model

Represents collection.


mongoose.model()

37. CRUD Operations


create()  
find()  
findById()  
updateOne()  
deleteOne()

Core database actions.

38. SQL Databases

Use:


PostgreSQL  
MySQL

Via libraries like pg or sequelize.

PART 7 — Authentication

39. JWT

JSON Web Token for login sessions.

40. Login Flow


User login  
Generate token  
Send token  
Verify token

Standard API auth.

41. Password Hashing


bcrypt.hash()

Never store plain passwords.

42. Auth Middleware

Protect routes.


verifyToken()

PART 8 — Validation

43. express-validator

Validates request input.

Prevents bad data.

PART 9 — File Upload

44. Multer

Handles file uploads.


multer()

Used for images/docs.

PART 10 — Environment Variables

45. dotenv


require("dotenv").config();

Stores secrets safely.

PART 11 — Async Programming

46. async / await


await dbCall();

Simplifies promises.

47. try / catch

Handles async errors.

PART 12 — Logging

48. Console Logs

Basic debugging.

49. Winston

Professional logging.

Used in production.

PART 13 — Testing

50. Jest

Unit testing.

51. Supertest

API testing.

PART 14 — Security

52. Helmet

Sets HTTP headers.

53. CORS

Controls cross-origin requests.

54. Rate Limiting

Prevents abuse.

PART 15 — Deployment

55. Build Server


node index.js

56. Production Tools


PM2  
Docker  
Nginx  
Cloud

57. Reverse Proxy

Nginx routes traffic.

PART 16 — Advanced Topics

58. WebSockets

Real-time communication.

59. Redis

Caching layer.

60. Kafka

Message queues.

61. Microservices

Split backend into services.