Koa Js

What is koaJs?

Koa is a new web framework designed by the team behind Express, which aims to be a smaller, more expressive, and more robust foundation for web applications and APIs.Koa uses asynchronous functions to help eliminate the need for callbacks and significantly improves error handling. Koa’s core does not include any middleware and instead provides an intuitive set of tools for developing servers quickly and easily.

It's better to learn koa if You generally like being ahead of the curve and on the bleeding edge, and if Your project needs to be future-proof, long-lived, and easy to maintain in the longer run

Features of KoaJs

1. Koa.js is cutting-edge and future-proof. Compared to other Node.js frameworks
2. KoaJs build is based on ES6 which makes the development of complex applications simpler by providing many new classes and modules. This helps developers in creating maintainable applications.
3. Koa.js uses a context object that encapsulates request and response objects.
4. Koa.js has a built-in catchall for errors that help prevent website crashes
5. Koa.js has a small footprint compared to other Node.js frameworks. This helps developers write thinner middleware.
6. Koa.js uses ES6 generators to simplify synchronous programming and facilitate the flow of controls. These generators can also be used as functions to control code execution on the same stack.

Pros and Cons

pros

• Extremely lightweight
• No callback hell
• Cleaner, more readable async code.
• Robust routing
• ES6 generators will tidy up the code and make it more manageable by removing the chaos created by all those callbacks.
• It provides an excellent user experience.

cons

• Koa uses generators that are not compatible with any other type of Node.js framework middleware
• The KoaJs open source community is relatively small
• Koa uses generators that are not compatible with any other type of Node.js framework middleware

Let's create a server using the KoaJs framework

First, create a new directory for your application, then, using the terminal, navigate to the directory of your app and run

npm init

To create a Node.js package

npm i koa

Then navigate to the index file and write the code below

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

app.listen(3000, () => {console.log('Server running at PORT 3000')})

Now the server will run on port 3000

Then to start the server

npm start

Creating Routes using KoaJs

koa.js does not handle routing by default. instead, it uses a middleware library Known as Koa Router. To implement routes in our server we have to install the Koa router library.

npm install koa-router

Then import the Koa router module onto your index file and add your desired routes. Below is a code example to demonstrate route creation using Koa.js.

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(3000, () => console.log('Server running at PORT 3000'))

Start the server again and test the route by sending a request from the browser.

Handling Responses in Koa.Js

Koa response objects are embedded in their context object. This indicates that the answer object is accessed through the context object. To explain how to handle replies, let’s use a route specification 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

To handle errors you can add middleware early in your index file. The code below includes the error middleware in our server

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"
})

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

app.listen(3000, () => console.log('Server running at PORT 3000'))

To test this let’s modify the home route method to throw an error when the route is called.

router.get('home', '/', (context) => {
  context.throw('error message', 500)
})

Now you can run the server.