What is Koa?

Koa is a newly popular Node.js framework created by the team at Express. It was built to be a more expressive, minimalist, and modern version of its predecessor. As a matter of fact, because of its embrace of modern development techniques in JavaScript, it has been referred to by some people as Express 5.0 in spirit.

Development on the Koa framework started sometime in late 2013 by the same team behind Express. It was decided that adding too many breaking changes to Express would be undesirable; hence, the team decided to take the new ideas it had to create a new framework, while development continued on Express itself in parallel. Koa was initially written to leverage the async goodness of the then-newly introduced JavaScript generators. Since then, Koa has been rewritten using the more modern async...await, making the code base even cleaner.

With around 2K LOC (lines of code), Koa can boast a very minimalistic code footprint. Koa is also very unopinionated; in fact, it does not ship with any middleware out of the box. Instead, it leaves these decisions to the developers. Developers can choose to either build out the middleware they need or take advantage of the ones built by other developers that are publicly available online.

By making use of the modern JavaScript async… await syntax, Koa allows developers to escape callback hell and handle errors better. Its futuristic approach to development in JavaScript makes it a choice for developers who enjoy trying out new things. If you are unfamiliar with what async… await is, not to worry, we will be covering it in following chapters.