Application-level Middleware in an Express Js

• Let's create a complete example of an application-level middleware in an Express.js application. In this example, we'll create middleware that logs information about incoming requests.

• Project Structure: Create a project structure with the following directories and files:

    - my-express-app/

        - middlewares/

            - requestLogger.js

        - routes/

            - index.js

        - app.js

        - package.json

• Middleware File (`requestLogger.js`): Create an application-level middleware that logs information about incoming requests:

    // middlewares/requestLogger.js

    const requestLogger = (req, res, next) => {

        console.log(`[${new Date().toISOString()}] ${req.method} ${req.url}`);

        next(); // Call the next middleware in the stack

    };

    module.exports = requestLogger;

• Route File (`index.js`): Create a route file in the `routes` directory:

    // routes/index.js

    const express = require('express');

    const router = express.Router();

    router.get('/', (req, res) => {

        res.send('Hello from the index route!');

    });

    module.exports = router;

• Express App (`app.js`): Set up the Express.js application and use the application-level middleware:

    // app.js

    const express = require('express');

    const requestLogger = require('./middlewares/requestLogger');

    const indexRoute = require('./routes/index');

    const app = express();

    const PORT = 3000;

    // Use the application-level middleware for all routes

    app.use(requestLogger);

    // Use the index route

    app.use('/', indexRoute);

    app.listen(PORT, () => {

        console.log(`Server is running on http://localhost:${PORT}`);

    });

• Run the Application: Run your application using the command:

    node app.js

• Visit `http://localhost:3000` in your browser. In the console where you started the server, you should see log entries with information about incoming requests, including the timestamp, HTTP method, and URL.

• This example demonstrates the use of an application-level middleware (`requestLogger`) in an Express.js application. The middleware logs information about incoming requests for all routes, providing a centralized way to capture request details before they reach the route handlers.