1. Logging Requests
Logging is one of the most common middleware tasks—it helps track incoming requests and responses.
Example:
const express = require('express');
const app = express();
// Custom logger middleware
app.use((req, res, next) => {
const start = Date.now();
console.log(`${req.method} ${req.url} at ${new Date().toISOString()}`);
res.on('finish', () => {
const duration = Date.now() - start;
console.log(`${req.method} ${req.url} - ${res.statusCode} (${duration}ms)`);
});
next();
});
app.get('/', (req, res) => {
res.send('Hello, world!');
});👉 Alternatively, you can use morgan, a popular logging middleware:
npm install morganconst morgan = require('morgan');
app.use(morgan('dev'));2. Error Handling
Express has built-in error handling middleware. Any middleware with 4 arguments (err, req, res, next) is treated as an error handler.
Example:
// Simulated error
app.get('/error', (req, res, next) => {
const err = new Error('Something went wrong!');
err.status = 500;
next(err);
});
// Error-handling middleware
app.use((err, req, res, next) => {
console.error(err.stack);
res.status(err.status || 500).json({
message: err.message || 'Internal Server Error',
});
});👉 Always place error handlers at the end of middleware stack.
3. Measuring Response Time
To measure how long each request takes, you can wrap timing logic in middleware.
Example:
app.use((req, res, next) => {
const startHrTime = process.hrtime();
res.on('finish', () => {
const diff = process.hrtime(startHrTime);
const time = diff[0] * 1e3 + diff[1] / 1e6; // in ms
console.log(`Response time for ${req.method} ${req.url}: ${time.toFixed(2)}ms`);
});
next();
});👉 Or use the response-time package:
npm install response-timeconst responseTime = require('response-time');
app.use(responseTime());
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