Introduction to Koa.js

Mohammed Rishard
Geek Culture
Published in
5 min readMar 28, 2021

What is koa.js?

Koa.js is an open-source, minimal, and flexible Node.js web framework developed by the creators of Express.js. They term Koa.js as the next level Node.js framework. Koa.js official website mentions koa.js as a smaller, more expressive, and more robust foundation for web applications and APIs. Koa eliminates callbacks and significantly improves error management by using async functions. Koa’s core doesn’t have any middleware, but it does include an elegant collection of methods for writing servers quickly and easily.

The key feature of Koa.js is the use of ES6 generators which means a program written using Koa.js will have fewer callbacks while behind the scenes it uses the asynchronous code we’ve come to know from Node.js but still the code is noticeably different and it is much simpler, cleaner and easier to grasp.

Features of Koa.js

Koa.js has its own distinguishing characteristics that make it more expressive and developer-friendly. Some of the features are –

1. It is modern and futuristic.

It is built based on ES6 specifications. By having many new classes and modules, ES6 makes it easier to build any complex program. As a result, it aids developers in the development of maintainable apps that remain valid over time.

2. It has a small footprint.

Compared to other Node.js frameworks Koa.js has a smaller footprint. This helps developers to write thinner and better middleware. They do, however, have the option of expanding the system to satisfy the needs of various projects by plugging in a number of modules.

3. It uses ES6 generators

It is used to simplify synchronous programming and facilitates both upstream and downstream flow of controls.

4. Better Error handling

By using middleware more efficiently, Koa.js simplifies and improves error handling. The framework’s built-in catchall for errors assists developers in avoiding website crashes. Even without writing additional code, programmers may report errors with a simple ‘try/catch’ command. Developers can also configure error handling in Koa.js by simply modifying the default setting.

5. It uses a context object

Koa.js also helps developers to use Context to encapsulate the vanilla response and request objects into a single object. The unified object makes it easier for developers to create web apps and APIs by including a number of useful methods and assessors. This context is a NodeJS object that encapsulates the request and response into a single object with several methods for writing web applications and APIs.

Pros of Koa.js

1. Koa increases interoperability and robustness while still making middleware creation more fun.

2. Koa is extremely light with just 550 lines of code.

3. ES6 generators will tidy up the code and make it more manageable by removing the chaos created by all those callbacks.

4. It provides a very good user experience.

5. Cleaner, more readable async code.

6. No callback hell

Cons of Koa.js

1. The open source community is relatively small.

2. Not compatible with Express-style middleware.

3. Koa makes use of generators that are incompatible with all other Node.js framework middleware.

Express.js vs Koa.js

Working on Koa.js is similar to working on Express.js because both these frameworks are developed by the same team. Koa is a very light and flexible system that can be moulded to suit the application requirement due to the absence of unnecessary boilerplate code and middleware. The inclusion of libraries increases the application’s modularity.

Koa removes callback hell and simplifies error management by using promises and async features. Instead of the node’s req and res objects, it exposes its own ctx.request and ctx.response objects.

Express, on the other hand, adds additional properties and methods to node’s req and res objects, as well as many other framework features including routing and templating that Koa lacks.

How is Koa different from Express?

· No callback hell

· Absence of boilerplate codes

· Better overall user experience

· Better error handling using try/catch

· Koa depends less on middleware

· Koa is more modular

· Routing is not available, unlike Express.

· Proper Stream handling

Hello World

Let’s try to display the most famous “Hello World” using Koa.js

In order to use koa.js, you need to have node.js installed on your computer. You can check whether Node.js has been installed by typing the below code in the terminal.

If it returns the version then that means you have already installed Node.js. If it returns “Command not found” please download and installnode.js from

Then create a new project and then create a JavaScript file and install the Koa package. You can type the below code in the terminal of your project folder to install the Koa.js package.

After the package has been successfully installed type the below code in your JavaScript file to display Hello World in the browser.

Now you can start the server by typing the below code in the terminal.

In the above code server is the name of the JavaScript file (server.js) that I created. In order to run you can type the name of the file you created, instead of the word server in the above example.

After you have started the server, open the browser and type localhost:3000 to view the output in the browser.

Congratulations! You have successfully created your first program using Koa.js

If you want to find out more about Koa.js, refer to its website or find it on Github