Handling 404 Errors in Express.js

 Introduction:

Handling 404 errors is an essential part of building web applications with Express.js. When a requested resource is not found, it's important to provide a meaningful response to the client. In this blog post, we'll explore how to handle 404 errors and return JSON responses using Express.js.

Setting up the Express Application:

Before we dive into error handling, let's set up a basic Express.js application:

const express = require('express');

const app = express();

// Your existing routes here...

// Middleware for handling 404 errors

app.use(function(req, res, next) {

  res.status(404).json({ error: 'Page not found' });

});

// Start the server

app.listen(3000, function() {

  console.log('Server started on port 3000');

});

Handling 404 Errors:

To handle 404 errors, we can use the built-in middleware app.use to capture all requests that do not match any existing routes. Here's an example of how we can achieve this:

app.use(function(req, res, next) {

    res.status(404).json({ error: 'Page not found' });

  });

In this example, the middleware is added after defining all your existing routes. When none of those routes match a request, the middleware will execute and return a JSON response with a 404 status code and an error message indicating that the page was not found.

Customizing the Error Response:

You can customize the JSON response according to your needs. Feel free to add additional properties to the JSON object, such as an error code or a more detailed description of the error.

Conclusion:

Handling 404 errors is crucial for providing a good user experience in web applications. With Express.js, it's straightforward to handle these errors and return JSON responses. By following the steps outlined in this blog post, you'll be able to ensure that your application gracefully handles 404 errors and communicates them effectively to the client.

Remember to place the 404 error handling middleware after all your existing routes in your Express application.