How to Fix Middleware Not Working in Express: Common Causes & Solutions

Middleware in Express may not work if it is not properly registered with app.use() or if the middleware function does not call next(). Also, middleware order matters; ensure middleware is added before routes that need it.

Why This Happens

Middleware might not work because it is either not added correctly to the Express app or it does not call next() to pass control. Another common cause is placing middleware after route handlers, so it never runs.

javascript

const express = require('express');
const app = express();

// Middleware defined but not used
function logger(req, res, next) {
  console.log('Request received');
  // next() missing here
}

app.get('/', (req, res) => {
  res.send('Hello World');
});

app.listen(3000);

Output

When you visit '/', the console does NOT log 'Request received' because middleware is not used and next() is missing.

The Fix

Register middleware with app.use() before your routes and ensure the middleware calls next() to continue the request cycle.

javascript

const express = require('express');
const app = express();

// Correct middleware with next()
function logger(req, res, next) {
  console.log('Request received');
  next();
}

// Use middleware before routes
app.use(logger);

app.get('/', (req, res) => {
  res.send('Hello World');
});

app.listen(3000);

Output

Console logs 'Request received' on every request, and the browser shows 'Hello World'.

Prevention

Always add middleware before routes that depend on it. Make sure every middleware calls next() unless it ends the response. Use linting tools to catch missing next() calls. Structure your app to clearly separate middleware and routes.

Related Errors

Other common middleware issues include:

• 404 Not Found because middleware that handles static files or parsing is missing.
• Headers already sent error when middleware sends a response but also calls next().
• Order issues where authentication middleware runs after routes, allowing unauthorized access.

Key Takeaways

Always register middleware with app.use() before defining routes.

Ensure middleware functions call next() to continue processing.

Middleware order affects whether it runs; place it before routes that need it.

Use linting tools to detect missing next() calls in middleware.

Test middleware behavior by checking console logs or response changes.