Koa.js
Koa.js is a lightweight, modern web framework for Node.js designed by the creators of Express.js. It uses async/await functions to eliminate callback hell and provides a robust set of features for building web applications and APIs. Its minimalistic core allows developers to add only the middleware they need, making it highly modular and flexible.
Developers should learn Koa.js when building scalable and maintainable web applications or APIs in Node.js, especially for projects requiring fine-grained control over request/response handling. It's ideal for modern JavaScript development due to its async/await support, which simplifies error handling and middleware chaining compared to callback-based frameworks. Use cases include RESTful APIs, single-page applications, and microservices where performance and modularity are priorities.