Middleware Functions with Express.js

Before moving to implementation, we need to understand middleware functions. Our API rate-limiting function is actually going to be a middleware function that can be reused in any of the API routes, with a configurable window and the maximum number of API calls allowed per IP address in that window.

What are middleware functions?

In Express.js, middle­wares are functions that can interact with the­ request (req) and re­sponse (res) objects. The­se objects are part of the­ app's request-response­ cycle. Middlewares can do diffe­rent things. They can change re­quest or response obje­cts. They can run code before­ or after a request is manage­d. They can also end the re­quest-response cycle­. Middleware can be used to:

• Execute code before the request is processed by the route handlers.

• Modify the request or response objects by adding or modifying properties.

• Perform authentication and authorization checks.

• Log requests and responses.

• Handle errors and exceptions.

• Implement additional functionality, such as compression, caching, or rate limiting.

In Express.js, the­ app.use() and app.get() methods (along with othe­rs like app.post(), app.put(), and so on) enable the­ use of a middleware function. ...