Koa JS Router Example using koa-router package

Routes are an important aspect to build any web application. However, KoaJS does not support routes as part of the core module. Therefore, we have to use an external module to enable routing. In this post, we will look at a basic Koa JS Router Example using the koa-router package.

If you are totally new to KoaJS, I will recommend you to go through this post on getting started with KoaJS.

1 – Installation of KoaJS Router Package

Unlike ExpressJS, Koa does not come with in-built router handling capability.

However, assuming that you already have a KoaJS application, we only need to install another package to work with routers.

$ npm install koa-router

Once the package installation is complete, we are ready to tweak our application to utilize the koa-router package.

2 – Implement a KoaJS Router Example

Let us implement a simple GET route example.

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

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

router.get('/greetings', (ctx, next) => {
  ctx.body = "Hello, World from Router"
});

app.use(router.routes())

app.listen(3000, function(){
   console.log('Server running on https://localhost:3000')
});

Let us understand what is happening in the above example.

• We first import the necessary packages. This includes koa and koa-router.
• Next, we create a Koa application instance using the constructor and new keyword.
• Also, we create an instance of the koa-router.
• Now, we can attach the route definitions to the router instance. For example, to attach a GET route, we call router.get() function. This function takes the route path as input and a callback function that contains the Koa application context.
• Within the callback, we set the response body to the required greeting message.
• Moving on, we call app.use() to attach the route definitions to the KoaJS middleware stack.
• Finally, we call app.listen() to start the application on port 3000.

Note here that the Koa Context is a special object that encapsulates the request and response objects of NodeJS into a single object. In KoaJS, a context instance is created per request and is referenced in the middleware as the receiver or the ctx identifier.

If we start the application at this point and visit http://localhost:3000/greetings, we will be able to see the greeting message in the browser.

Conclusion

We have successfully looked at a Koa JS Router Example using koa-router middleware package. We also explore the concept of context in a KoaJS application.

Since the core KoaJS framework does not provide features such as router, the base framework is quite minimal. This makes it extremely flexible.

Want to create dynamic routes? Check out this post on how to handle route parameters in KoaJS.

If you have any comments or queries about this post, please feel free to mention them in the comments section below.