KOA a web framework which is designed by the team behind Express, which aims to be a smaller, more expressive, and more robust foundation for web applications and APIs. Koa was created by the original creator of express. Koa is intended to solve a lot of the problems in express, like having to do monkey patching which is where one modify prepackaged code. It’s an extremely elegant, clean, and efficient way to program asynchronously.
Koa is more lightweight and more modular than express in few terms. One can create an app and the good point is there’s not tons of stuff already there, it’s a completely empty application and one can only use the stuff they want to use. If want a logger to print requests and responses in koa, one will add the koa-logger middleware. If one want static pages then add the koa-static middleware. Adding middleware takes one line of code and is super easy. The bottom line is that if we learn to code with generators and in Koa we are able to write in 10 lines what would have before taken like 30 lines. So, Koa.js is a powerful server framework for Node.js to build. Koa is a little tougher also because it requires some background knowledge in generators and promises. Koa.js is focused on creating web applications and APIs with improved performance. Comparing to Express, which is based entirely on callback technology, separating out request and response objects, Koa main advantage is the usage of ES6 Generator feature. Koa generator is an excellent way to avoid callbacks, help developers to manage the code easier with the component-based building blocks and handle errors efficiently and hence a good alternate of Express.