Building APIs with Koa.js

Introduction

Koa.js is a modern web framework for Node.js designed by the creators of Express. It aims to be a smaller, more expressive, and more robust foundation for web applications and APIs.

Prerequisites

• Basic knowledge of JavaScript and Node.js.
• Familiarity with REST APIs and how they work.
• Node.js installed on your machine.

Installation

To start building APIs with Koa.js, you first need to install Koa. You can do this using npm:

npm install koa koa-router

Creating a Basic API

Here’s how to create a simple Koa application:

const Koa = require('koa');
const Router = require('koa-router');

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

router.get('/', ctx => {
    ctx.body = 'Hello, Koa!';
});

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

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

Middleware in Koa

Koa uses middleware to handle requests. Middleware functions can be composed to create a request/response handling chain. Here’s an example of middleware usage:

app.use(async (ctx, next) => {
    console.log('Request received:', ctx.request.method, ctx.request.url);
    await next();
});
        

Error Handling

Proper error handling is crucial for any API. Here’s how you can handle errors in Koa:

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

Best Practices

• Keep your middleware small and focused.
• Use async/await for better readability.
• Implement proper logging for debugging.
• Always validate user input.
• Use environment variables for configuration.

FAQ