Error Handling In Expressjs | Node Express

1. Introduction

Error handling is a critical part of building robust applications with Express.js. Proper error handling ensures that applications can gracefully handle unexpected situations and provide meaningful feedback to users.

2. Types of Errors

In Express.js, errors can be classified into several categories:

Client Errors (4xx): These are errors related to the client's request.
Server Errors (5xx): These are errors that occur on the server side.
Programming Errors: These occur due to bugs in the code, such as syntax errors or reference errors.

3. Error Handling Middleware

Express provides a built-in mechanism for handling errors using middleware. An error handling middleware function is defined in the same way as other middleware, but it has four arguments instead of three: function (err, req, res, next).

Example Error Handling Middleware


app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).send('Something broke!');
});

This middleware will log the error stack to the console and send a 500 status code response to the client.

4. Best Practices

To effectively handle errors in your Express applications, consider the following best practices:

Use centralized error handling middleware.
Send appropriate HTTP status codes.
Log errors for debugging purposes.
Don't expose sensitive information in error messages.
Test error scenarios thoroughly.

5. FAQ

What should I do if I encounter an uncaught exception?

Use process event listeners like process.on('uncaughtException', callback) to handle uncaught exceptions. However, it's better to handle exceptions gracefully rather than allowing them to crash the app.

How do I handle async errors in Express?

For async routes, you can use a try-catch block or a utility function to catch errors and pass them to the next middleware.

Can I customize error responses?