Express.js Basics: Setting Up Your First API

New to backend development? Let's build a simple REST API with Express.js from scratch.

Why Express?

Express.js has been around forever (in JavaScript years), and there's a reason it's still the go-to for Node.js APIs. It's minimal, flexible, and has a massive ecosystem.

This is Part 1 of a series where we'll build out a complete backend.

Getting Started

mkdir my-api
cd my-api
npm init -y
npm install express

Hello World

Create `index.js`:

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

app.get('/', (req, res) => {
  res.json({ message: 'Hello World!' });
});

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

Run it:

node index.js

That's it. You have an API.

Adding Routes

Let's add a simple resource - users:

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

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

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

Handling POST Requests

Need to parse JSON bodies first:

app.use(express.json());

// POST new user
app.post('/api/users', (req, res) => {
  const { name } = req.body;
  
  if (!name) {
    return res.status(400).json({ error: 'Name is required' });
  }
  
  const newUser = {
    id: users.length + 1,
    name
  };
  
  users.push(newUser);
  res.status(201).json(newUser);
});

Project Structure

As your API grows, organize it:

my-api/
├── index.js
├── routes/
│   └── users.js
├── controllers/
│   └── userController.js
├── middleware/
│   └── errorHandler.js
└── package.json

What's Next

In the next post, we'll cover:

• Middleware and error handling
• Input validation
• Connecting to a database

The concepts here apply whether you're building a side project or a production API. Start simple, add complexity as needed.

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