ExpressJS Middleware

ExpressJS Middleware refers to functions that have access to the request object (req), the response object (res), and the next middleware function in the application's request-response cycle.
Middleware functions can execute any code, make changes to the request and response objects, end the request-response cycle, or call the next middleware function in the stack.
ExpressJS Middleware plays a crucial role in handling requests, performing tasks such as logging, authentication, data parsing, error handling, and more.

1. Overview

ExpressJS Middleware acts as a bridge between incoming HTTP requests and route handlers, allowing developers to perform various tasks before or after routing requests to specific endpoints.

Middleware functions can be used to:

Modify request and response objects.
Execute additional code before passing control to the next middleware function.
Terminate the request-response cycle prematurely.
Invoke the next middleware function in the stack.

Middleware functions are executed sequentially in the order they are defined, allowing developers to create a pipeline of middleware to handle requests.

2. Example

Here's an example of a simple middleware function that logs information about incoming requests:

 // Logger Middleware
const loggerMiddleware = (req, res, next) => {
    console.log(`[${new Date().toISOString()}] ${req.method} ${req.url}`);
    next();
};

// Attach Middleware to Express App
app.use(loggerMiddleware);

In this example, the loggerMiddleware function logs the timestamp, HTTP method, and URL of incoming requests before passing control to the next middleware function.

3. Built-in Middleware

ExpressJS provides several built-in middleware functions to handle common tasks such as serving static files, parsing request bodies, and handling errors. These middleware functions can be easily integrated into Express applications using the app.use() method.

4. Conclusion

ExpressJS Middleware is a powerful feature that allows developers to add functionality and modify request/response objects in the request-response cycle. By using middleware functions, developers can create flexible and extensible Express applications that handle a wide range of tasks efficiently.