How to Build a Simple REST API with Node.js and Express.

Building a REST API is a fundamental skill for any web developer. In this guide, I'll walk you through creating a simple REST API using Node.js and Express — a fast and minimal web framework for Node.

Step 1: Create Your Project Folder and Initialize

Open your terminal.
Create a new folder for your project and move inside it:

mkdir simple-api
cd simple-api

Initialize a new Node.js project. This creates a package.json file to manage dependencies:

npm init -y

Step 2: Install Express

Express makes handling HTTP requests straightforward.

Install Express in your project by running:

npm install express

Step 3: Create Your Server File

Inside your project folder, create a new file called index.js.
This file will contain your server code.

Step 4: Write Basic Server Code

Open index.js and add the following code:

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

app.use(express.json()); // Parse JSON request bodies

app.listen(PORT, () => {
  console.log(`Server running on http://localhost:${PORT}`);
});

This code sets up a basic Express server that listens on port 3000.

Step 5: Add Sample Data

Add a simple list of users inside index.js to work with:

let users = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' }
];

Step 6: Create API Endpoints

Add these routes inside index.js after the sample data:

Get all users

app.get('/users', (req, res) => {
  res.json(users);
});

Get a single user by ID

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

Add a new user

app.post('/users', (req, res) => {
  const user = {
    id: users.length + 1,
    name: req.body.name
  };
  users.push(user);
  res.status(201).json(user);
});

Update a user by ID

app.put('/users/:id', (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));
  if (!user) return res.status(404).send('User not found');

  user.name = req.body.name;
  res.json(user);
});

Delete a user by ID

app.delete('/users/:id', (req, res) => {
  users = users.filter(u => u.id !== parseInt(req.params.id));
  res.sendStatus(204);
});

Step 7: Run Your API Server

Save your index.js file.
Run your server from the terminal:

node index.js

You should see:
Server running on http://localhost:3000

Step 8: Test Your API

Use a tool like Postman or your browser and terminal to test the endpoints:

Get all users:
Visit http://localhost:3000/users in your browser or send a GET request.
Get a user by ID:
GET http://localhost:3000/users/1
Add a user:
Send a POST request to http://localhost:3000/users with JSON body:
{ "name": "Charlie" }
Update a user:
Send a PUT request to http://localhost:3000/users/1 with JSON body:
{ "name": "Alice Updated" }
Delete a user:
Send a DELETE request to http://localhost:3000/users/1

Final Thoughts

Congratulations! You just built a simple REST API using Node.js and Express. From here, you can extend this API by adding a database, authentication, or other features.