Middleware in Express.js is a function that is invoked by the Express.js routing layer before the final request handler is executed. Middleware functions can perform a variety of tasks, such as logging requests, validating data, and serving static files.
Example:
const express = require(‘express’);
const app = express();
// Logging middleware
app.use((req, res, next) => {
console.log(`${req.method} request for ${req.url}`);
next();
});
// Serve static files
app.use(express.static(‘public’));
// Handle requests
app.get(‘/’, (req, res) => {
res.send(‘Hello World!’);
});
app.listen(3000);
console.log(‘Express app running on port 3000’);