Koa vs Express
What is KoaJs ?
KoaJs is a Node.js web application framework with a powerful collection of capabilities for online and mobile apps. It’s an open source framework created and maintained by the same people that brought you ExpressJs, the most popular node web framework.
What is ExpressJs ?
Express is a nodeJs web application framework with a wide range of functionality for developing online and mobile apps. It’s used to create single-page, multi-page, and hybrid web apps.
It’s a NodeJs layer that supports in the management of servers and routes.
Key Differences in between Koa Vs Express
Koa is a more lightweight version of Express. It’s a middleware framework without all of the extra modules (for routing and templating) found with Express.
Koa was created by the same team that created Express. Many people consider Koa to be “Express 5.0,” given its development was heavily influenced by ownership concerns with the original Express.
Node Improvement vs. Node Replacement
Express is a NodeJS web framework. Express adds useful methods and features to Node’s req and res objects.
For example, Express adds things like req.method and req.headers() to the http req object and res.sendFile() to the http res object.
Koa is a NodeJS middleware framework. Koa uses its own context to replace or remove Node’s req and res objects.
For example, context.body = result specifies the request’s response content.
The Express middleware chain uses callbacks, whereas the Koa middleware chain uses Promises. This is why, with Express, we define errorMiddleware last and handleError first.
Express is heavier than Koa. Like Express, Koa does not feature router or view engine components. These modules are available individually and may be readily combined. You’ll see that for our Koa example, we had to include koa-router individually, but this was already included with Express.
Unlike Express, Koa does not come with built-in support for routing, templating, sending files, JSONP, and other features.
For clearer code, Koa uses Generator functions and async/await. While this helps avoid “callback hell” when using Express in Node v7+, it’s less noticeable when using async/await with Express.
Less popular (but growing)
Express has a far larger following than Koa. While Koa is becoming more popular, Express is still the most popular web application framework, with over 11 million weekly downloads.
This means that Express has a lot more documentation than Koa. Coming into a project, NodeJS engineers are more likely to have expertise with Express than Koa.
When to use Express over Koa
When you need support for routing and templating in a browser-based application, use Express.
If your development team is new and need more community help or documentation, choose Express.
When to use Koa over Express
When your application isn’t browser-based and you don’t need routing or templating, Koa is the way to go.
If you want to emphasize performance, go with Koa (more lightweight). While the speed improvements may be minor, Koa has proved to be somewhat quicker than Express in several tests.
Remember that Koa was created by the same people that created Express. Koa is simply a stripped-down version of Express that lacks routing and templating out of the box.
Express is a lot older than Koa. It has a more established community. Express has more documentation and examples than Koa.
While Koa makes it easier to write middleware, Express with async/await avoids “callback hell” and has a comparable syntax.