Koa.js

What is Koa.js?

Koa.js is a simple and versatile Node.js web development architecture that offers a versatile range of features for web and mobile applications. It is an open-source platform created and maintained by the same people who brought you Express.js, the most common node web framework. You will get rid of callbacks and massively improve error management with Koa. Koa does not have any middleware, but it does include an elegant collection of methods for writing servers quickly and easily. Unlike other Node.js frameworks, Koa.js is built using ES6, which simplifies the construction of complex applications by including a slew of new classes and modules. This aids developers in the development of maintainable software.

Features of Koa.js

· In comparison to other Node.js frameworks, Koa.js has a small footprint. This makes it easier for developers to create middleware that is lighter in weight.

· A built-in error catchall in Koa.js helps avoid website crashes.

· A context object, which is an encapsulation of request and answer objects, is used by Koa.js.

· Koa.js makes use of ES6 generators to make synchronous programming easier and the flow of controls more fluid. These generators can also be used to manage the execution of code on the same stack as functions.

Building a server in the Koa.js framework

Create a new directory for your application first, then use the terminal to navigate to that directory and run

To make a package in Node.js.

npm init

Then install Koa.js

npm i koa

After that, use your preferred code editor to navigate to the index file in your app’s directory and write the code below to build the server.

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

app.listen(3100, () => {console.log('Server running at PORT 3100')})

Building routes in Koa.js

By default, Koa.js does not perform routing. Instead, it employs the Koa Router middleware library. So, in order to introduce routes in our server, we must first install the Koa router library using the snippet below.

npm install koa-router

Then, in your index file, import the Koa router module and add your desired routes. A code example of route construction using Koa.js is given below.

const koa = require('koa')
const koaRouter = require('koa-router')// importing Koa-Router

const app = new koa()
const router = new koaRouter()

router.get('home', '/', (context) => {
  context.body = "Welcome to my Koa.js Server"
})

app.use(router.routes())
  .use(router.allowedMethods())// registering routes to the application

app.listen(3100, () => console.log('Server running at PORT 3100'))

Handling Responses in Koa.js

The context object contains Koa response objects. This implies that the response object is accessed from the context object. To explain how to handle responses, let’s use a route definition like the one above.

router.get('home', '/', (context) => {
  context.status = 200 //This is the response status
  context.body   = "Welcome to my Koa.js Server" // This is the response body
})

Handling errors in Koa.js

Add an error middleware early in your index file to manage errors in Koa. Only errors identified after the middleware can be caught, so it must be defined early. Our server’s error middleware is used in the code below.

const koa = require('koa')
const koaRouter = require('koa-router')// importing Koa-Router

const app = new koa()
const router = new koaRouter()

app.use( async (ctx, next) => {
  try {
    await next()
  } catch(err) {
    console.log(err.status)
    ctx.status = err.status || 500;
    ctx.body = err.message;
  }
})

router.get('home', '/', (context) => {
  context.body = "Welcome to my Koa.js Server"
})