I'd be happy to help you build a REST API with Express.js! Here's a complete setup for a CRUD application.

First, initialize your project and install dependencies:

mkdir my-api && cd my-api
npm init -y
npm install express cors
npm install -D nodemon

Now create your Express application with full CRUD endpoints:

const express = require('express');
const cors = require('cors');
const app = express();
const PORT = process.env.PORT || 3000;

// Middleware
app.use(cors());
app.use(express.json());

// In-memory data store
let items = [
  { id: 1, name: 'Item One', description: 'First item' },
  { id: 2, name: 'Item Two', description: 'Second item' }
];
let nextId = 3;

// GET all items
app.get('/api/items', (req, res) => {
  res.json({ success: true, data: items });
});

// GET single item
app.get('/api/items/:id', (req, res) => {
  const item = items.find(i => i.id === parseInt(req.params.id));
  if (!item) {
    return res.status(404).json({ success: false, message: 'Item not found' });
  }
  res.json({ success: true, data: item });
});

// POST create item
app.post('/api/items', (req, res) => {
  const { name, description } = req.body;
  const newItem = { id: nextId++, name, description };
  items.push(newItem);
  res.status(201).json({ success: true, data: newItem });
});

// PUT update item
app.put('/api/items/:id', (req, res) => {
  const item = items.find(i => i.id === parseInt(req.params.id));
  if (!item) {
    return res.status(404).json({ success: false, message: 'Item not found' });
  }
  item.name = req.body.name || item.name;
  item.description = req.body.description || item.description;
  res.json({ success: true, data: item });
});

// DELETE item
app.delete('/api/items/:id', (req, res) => {
  const index = items.findIndex(i => i.id === parseInt(req.params.id));
  if (index === -1) {
    return res.status(404).json({ success: false, message: 'Item not found' });
  }
  items.splice(index, 1);
  res.json({ success: true, message: 'Item deleted' });
});

app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

This gives you the following endpoints:

• GET /api/items — Retrieve all items
• GET /api/items/:id — Retrieve a single item
• POST /api/items — Create a new item
• PUT /api/items/:id — Update an existing item
• DELETE /api/items/:id — Delete an item

Run the server with node app.js or add "dev": "nodemon app.js" to your package.json scripts. Want me to add input validation next?