Build Your First REST API

Set Up the Project

mkdir first-api
cd first-api
npm init -y
npm install express
npm install -D nodemon

Update package.json to add a dev script:

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

Create the Base Server

Create index.js:

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

app.use(express.json());

const PORT = 3000;

// In-memory data store (resets on restart)
let posts = [
    { id: 1, title: 'Hello World', body: 'My first post' }
];

// GET / — sanity check
app.get('/', (req, res) => {
    res.json({ message: 'API is running' });
});

// GET /posts — list all
app.get('/posts', (req, res) => {
    res.json(posts);
});

// GET /posts/:id — single post
app.get('/posts/:id', (req, res) => {
    const id = parseInt(req.params.id);
    const post = posts.find(p => p.id === id);
    if (!post) {
        return res.status(404).json({ error: 'Post not found' });
    }
    res.json(post);
});

// POST /posts — create
app.post('/posts', (req, res) => {
    const { title, body } = req.body;
    if (!title || !body) {
        return res.status(400).json({ error: 'Title and body are required' });
    }
    const newPost = {
        id: posts.length ? posts[posts.length - 1].id + 1 : 1,
        title,
        body
    };
    posts.push(newPost);
    res.status(201).json(newPost);
});

// PUT /posts/:id — update
app.put('/posts/:id', (req, res) => {
    const id = parseInt(req.params.id);
    const post = posts.find(p => p.id === id);
    if (!post) {
        return res.status(404).json({ error: 'Post not found' });
    }
    const { title, body } = req.body;
    if (!title || !body) {
        return res.status(400).json({ error: 'Title and body are required' });
    }
    post.title = title;
    post.body = body;
    res.json(post);
});

// DELETE /posts/:id — remove
app.delete('/posts/:id', (req, res) => {
    const id = parseInt(req.params.id);
    const index = posts.findIndex(p => p.id === id);
    if (index === -1) {
        return res.status(404).json({ error: 'Post not found' });
    }
    posts.splice(index, 1);
    res.status(204).send();
});

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

Start the Server

npm run dev

You should see:

API running at http://localhost:3000

Test with curl

Open another terminal and try each endpoint:

# List all posts
curl http://localhost:3000/posts

# Get one post
curl http://localhost:3000/posts/1

# Create a new post
curl -X POST http://localhost:3000/posts \
  -H "Content-Type: application/json" \
  -d '{"title":"New Post","body":"From curl"}'

# Update a post
curl -X PUT http://localhost:3000/posts/1 \
  -H "Content-Type: application/json" \
  -d '{"title":"Updated","body":"New content"}'

# Delete a post
curl -X DELETE http://localhost:3000/posts/2

Each returns JSON — that's your working REST API. 🎉