Custom Middleware
Custom middleware is a software design pattern where developers create their own intermediary functions or components that process requests and responses in an application's execution pipeline. It sits between the client and server or between different layers of an application, intercepting and modifying data flow to add functionality like logging, authentication, or error handling. This pattern is commonly implemented in web frameworks, APIs, and distributed systems to enhance modularity and reusability.
Developers should learn and use custom middleware when they need to add cross-cutting concerns—such as request validation, rate limiting, or data transformation—that apply uniformly across multiple routes or services without cluttering core business logic. It's particularly useful in scenarios like building RESTful APIs with frameworks like Express.js or ASP.NET Core, where middleware can handle tasks like JWT authentication, CORS configuration, or request logging in a centralized, maintainable way. By decoupling these concerns, custom middleware improves code organization, reduces duplication, and simplifies testing and debugging.