Introduction to Koa.js

Koa.js is a lightweight and flexible Node.js web framework designed for building APIs and web applications. It was created by the same team behind Express.js and aims to provide a more expressive and robust foundation for web applications and APIs.

To install Koa.js, you need to have Node.js installed on your machine. You can use npm to install Koa as follows:

npm install koa

• Context (ctx): Represents the request and response objects. It provides a simplified API for accessing request data and sending responses.
• Middleware: Functions that have access to the request, response, and the next middleware function in the application’s request-response cycle.
• Async/Await: Koa leverages async functions, making it easier to work with asynchronous code and avoiding callback hell.

Middleware functions can perform various tasks such as logging, authentication, and error handling. The order of middleware is significant, as they are executed in the order they are defined.

const Koa = require('koa');
const app = new Koa();

app.use(async (ctx, next) => {
    console.log('Request received:', ctx.request.url);
    await next(); // Call the next middleware
    console.log('Response sent:', ctx.response.status);
});
            

Here’s a simple example of a Koa.js application:

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

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

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

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

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

• Use async/await for handling asynchronous operations.
• Organize middleware functions to maintain clarity and order.
• Perform error handling at the application level to capture all errors gracefully.