What are the differences between koa and express 4.0?

@denis 

Koa and Express are both popular web application frameworks for Node.js, but there are some key differences between them:

1. Middleware handling: In Express, middleware is handled in a linear, sequential manner using callbacks. In contrast, Koa uses a more modern and elegant approach by utilizing async/await or generator functions, allowing for better error handling and more readable code.
2. Context object: Koa introduces a new concept called the "context" object, which encapsulates the request and response objects, along with additional functionality like the request body parsing, routing, and error handling. This allows for more concise code and better encapsulation.
3. Lightweight core: Express has been around for quite some time and has accumulated various features over the years. As a result, Express has a larger codebase and more built-in functionality. On the other hand, Koa has a much smaller core and encourages the use of third-party middleware for additional functionality. This can be advantageous for developers who prefer a minimalistic approach and want more control over their application's dependencies.
4. Error handling: Koa has a built-in error handling mechanism that allows developers to catch and handle errors more easily. In Express, error handling is typically done using middleware or with try-catch blocks, which can be more cumbersome and error-prone.
5. Compatibility: Express has a larger community and ecosystem compared to Koa, which means there are more third-party modules, plugins, and resources available. Koa, being a newer framework, has a smaller community, but it is growing steadily.

Ultimately, the choice between Koa and Express depends on individual preferences and project requirements. Express is more mature and has a larger community, while Koa offers a more modern and elegant approach with better error handling capabilities.