• app.use (requestMiddleware)→>> every request mentioned after this will always pass through request Middleware
• order is important
• the middleware function must be before app.use()

Middleware refers to software or functions that sit between two layers of a system, typically handling requests, responses.

In the context of web development and frameworks, middleware is a piece of code that sits between the client (making requests) and the server (handling requests).

Middleware in Web Development:

1. Express.js (Node.js): In Express, middleware functions are executed in the order they are defined. They have access to the request object (req), the response object (res), and the next function in the application's request-response cycle. Middleware can:

   • Execute any code.
   • Make changes to the req and res objects.
   • End the request-response cycle.
   • Call the next() middleware function.

   Example:

   
   app.use((req, res, next) => {
     console.log('Middleware running');
     next();
   });
   
   

2. Next.js: In Next.js, middleware runs before the request is completed and can modify the request or response, such as checking authentication, modifying headers, or redirecting.

   Example:

   
   // middleware.js //
   
   export function middleware(request) {
     // Perform some checks or modifications
     return NextResponse.redirect(new URL('/login', request.url));
   }
   
   

3. Redux Middleware: In Redux, middleware intercepts actions before they reach the reducers, allowing you to perform side effects such as logging, making API calls, or modifying the action.

Common Uses of Middleware:

• Authentication and Authorization:
• Logging: Record details of requests and responses for debugging or analysis.
• Request Transformation: Modify incoming requests before they reach the handler (e.g., parsing JSON bodies).
• Response Transformation: Modify responses before they are sent back to the client.