Build a RESTful API with Koa.js: Complete Guide

Learn how to create a modern RESTful API using Koa.js, including setup, CRUD operations, authentication, and best practices.

Perfect for Node.js developers looking to build scalable APIs.

How to Build a RESTful API with Koa.js

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Building APIs has become an essential skill for modern web developers. While Express.js remains popular, Koa.js offers a more lightweight and modern approach to building Node.js applications. In this guide, we’ll explore how to create a RESTful API using Koa.js from the ground up.

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Setting Up Your Project

First, let’s create a new project and install the necessary dependencies:

mkdir koa-rest-api
cd koa-rest-api
npm init -y
npm install koa @koa/router koa-bodyparser

Creating the Basic Server

Let’s start with a simple server setup:

const Koa = require('koa');
const Router = require('@koa/router');
const bodyParser = require('koa-bodyparser');

const app = new Koa();
const router = new Router();

app.use(bodyParser());

// Basic error handling
app.use(async (ctx, next) => {
  try {
    await next();
  } catch (err) {
    ctx.status = err.status || 500;
    ctx.body = { error: err.message };
  }
});

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Implementing CRUD Operations

Here’s how to implement basic CRUD operations for a resource (let’s say, for books):

// In-memory storage for demonstration
let books = [];

// GET all books
router.get('/books', ctx => {
  ctx.body = books;
});

// GET single book
router.get('/books/:id', ctx => {
  const book = books.find(b => b.id === parseInt(ctx.params.id));
  if (book) {
    ctx.body = book;
  } else {
    ctx.status = 404;
    ctx.body = { error: 'Book not found' };
  }
});

// POST new book
router.post('/books', ctx => {
  const book = {
    id: books.length + 1,
    ...ctx.request.body
  };
  books.push(book);
  ctx.status = 201;
  ctx.body = book;
});

// PUT update book
router.put('/books/:id', ctx => {
  const index = books.findIndex(b => b.id === parseInt(ctx.params.id));
  if (index >= 0) {
    books[index] = {
      ...books[index],
      ...ctx.request.body
    };
    ctx.body = books[index];
  } else {
    ctx.status = 404;
    ctx.body = { error: 'Book not found' };
  }
});

// DELETE book
router.delete('/books/:id', ctx => {
  const index = books.findIndex(b => b.id === parseInt(ctx.params.id));
  if (index >= 0) {
    books.splice(index, 1);
    ctx.status = 204;
  } else {
    ctx.status = 404;
    ctx.body = { error: 'Book not found' };
  }
});

app.use(router.routes()).use(router.allowedMethods());

Adding Middleware for Authentication

Security is crucial for APIs. Here’s a simple authentication middleware:

const authMiddleware = async (ctx, next) => {
  const token = ctx.headers.authorization;
  if (!token || token !== 'your-secret-token') {
    ctx.status = 401;
    ctx.body = { error: 'Unauthorized' };
    return;
  }
  await next();
};

// Apply to specific routes
router.use('/books', authMiddleware);

Testing Your API

You can test your API using tools like Postman or curl. Here’s a quick curl example:

# Get all books
curl http://localhost:3000/books

# Create a new book
curl -X POST http://localhost:3000/books \
  -H "Content-Type: application/json" \
  -d '{"title": "The Great Gatsby", "author": "F. Scott Fitzgerald"}'

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Best Practices

Always validate input data
Use appropriate HTTP status codes
Implement rate limiting for production
Add comprehensive error handling
Document your API endpoints
Use environment variables for configuration

Conclusion

Koa.js provides a modern and elegant way to build RESTful APIs. Its middleware stack and async/await support make it a powerful choice for Node.js developers. As you continue building your API, remember to implement proper security measures and follow REST best practices.

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