How to Write a REST API in JavaScript in 30 Minutes: A Practical Guide

Introduction: REST API in Half an Hour — It's Real

REST API is the foundation of modern web interaction. Whether you're a frontend developer wanting to understand the backend, or a beginner who wants to quickly create their first server — this guide is for you. We'll break down how to write a full-fledged REST API in JavaScript (Node.js) literally in 30 minutes.

We use a minimal stack: Node.js and Express.js — the most popular framework for creating APIs. No extra code, only practice. By the end of the article, you will have a working server with CRUD operations (create, read, update, delete).

Step 1: Preparation and installing dependencies

First, make sure you have Node.js installed (version 14 or higher). You can download it from the official website. Check the installation:

node -vnpm -v

Create a project folder and navigate into it:

mkdir my-rest-apicd my-rest-api

Initialize the project and install Express:

npm init -ynpm install express

For convenience, install nodemon — it automatically restarts the server when code changes:

npm install --save-dev nodemon

Now open package.json and replace the "scripts" section with:

"scripts": {  "start": "node index.js",  "dev": "nodemon index.js"}

Great! Everything is ready for writing code.

Step 2: Writing the basic server and first endpoint

Create a file index.js in the project root. Let's start by importing Express and setting up the port:

const express = require('express');const app = express();const PORT = 3000;

// Middleware for parsing JSONapp.use(express.json());

// Simple test endpointapp.get('/', (req, res) => {  res.send('My REST API is working!');});

// Start the serverapp.listen(PORT, () => {  console.log(`Server running at http://localhost:${PORT}`);});

Start the server with the command:

npm run dev

Go to http://localhost:3000 in your browser — you should see the message "My REST API is working!".

Adding a database simulation

For simplicity, we will store data in memory (an array). In a real project, you would connect MongoDB or PostgreSQL, but this is sufficient for learning.

// Database simulationlet users = [  { id: 1, name: 'Alexey', email: 'alex@example.com' },  { id: 2, name: 'Maria', email: 'maria@example.com' }];let nextId = 3;

Step 3: Implementing CRUD operations

Now let's create full-fledged endpoints for working with users. We will implement four main HTTP methods: GET, POST, PUT, DELETE.

GET — retrieving all users

// Get all usersapp.get('/api/users', (req, res) => {  res.json(users);});

// Get user by IDapp.get('/api/users/:id', (req, res) => {  const id = parseInt(req.params.id);  const user = users.find(u => u.id === id);    if (!user) {    return res.status(404).json({ message: 'User not found' });  }    res.json(user);});

POST — creating a new user

// Create userapp.post('/api/users', (req, res) => {  const { name, email } = req.body;    // Simple validation  if (!name || !email) {    return res.status(400).json({ message: 'Name and email are required' });  }    const newUser = {    id: nextId++,    name,    email  };    users.push(newUser);  res.status(201).json(newUser);});

PUT — updating a user

// Update userapp.put('/api/users/:id', (req, res) => {  const id = parseInt(req.params.id);  const { name, email } = req.bod