404 Not Found handler in Express - Mini Project: Build & Apply

Express 404 Not Found Handler

📖 Scenario: You are building a simple Express web server. You want to handle requests to pages that do not exist by showing a friendly 404 Not Found message.

🎯 Goal: Create an Express app that responds with a 404 Not Found message for any request that does not match existing routes.

📋 What You'll Learn

Create an Express app instance

Add a basic route for the home page at '/'

Add a 404 handler middleware that catches all unmatched routes

Send a 404 status and a simple text message '404 Not Found' in the 404 handler

💡 Why This Matters

🌍 Real World

Web servers often need to handle requests to pages that do not exist. Showing a clear 404 Not Found message helps users understand the problem.

💼 Career

Knowing how to add middleware and handle 404 errors is a basic skill for backend developers working with Express or similar web frameworks.

1

Create Express app and home route

Write code to import Express, create an app instance called app, and add a GET route for '/' that sends the text 'Home Page'.

Express

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

// Your code here

Need a hint?

Use express() to create the app. Use app.get for the home route.

2

Add 404 handler middleware

Add a middleware function using app.use that takes req, res, and next parameters. This middleware will handle all unmatched routes.

Express

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

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

// Add 404 middleware below
// Your code here

Need a hint?

Use app.use with three parameters to catch all unmatched routes.

3

Set 404 status and send message

Inside the 404 middleware, set the response status to 404 using res.status(404) and send the text '404 Not Found' using res.send.

Express

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

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

app.use((req, res, next) => {
  // Set 404 status and send message
  // Your code here
});

Need a hint?

Chain res.status(404) and res.send('404 Not Found') to respond properly.

4

Start the server on port 3000

Add code to start the Express server by calling app.listen on port 3000.

Express

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

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

app.use((req, res, next) => {
  res.status(404).send('404 Not Found');
});

// Start server on port 3000
// Your code here

Need a hint?

Use app.listen(3000) to start the server.