Exploring Error Handling Middleware in Detail

In this lesson, we will be diving into the world of error handling middleware in Express JS.

What is Error Handling Middleware?

Error handling middleware in Express JS is a function that takes four arguments: err, req, res, and next. This function is used to handle errors that occur during the execution of the application.

How to Use Error Handling Middleware

To use error handling middleware in your Express JS application, you need to define a function that takes four arguments: err, req, res, and next. This function should be added as the last middleware in your application.

Here is an example of how to define an error handling middleware:

app.use(function(err, req, res, next) {
  console.error(err.stack);
  res.status(500).send('Something went wrong!');
});

Understanding the Structure of Error Handling Middleware

The err argument in the error handling middleware function contains the error object that was thrown by the previous middleware or route handler. The req argument contains the request object, the res argument contains the response object, and the next argument is a function that can be called to pass control to the next middleware in the stack.

Common Errors Handled by Error Handling Middleware

Some common errors that can be handled by error handling middleware include:

1. Internal server errors (HTTP status code 500)
2. Not found errors (HTTP status code 404)

Conclusion

Error handling middleware in Express JS is a powerful tool that can help you handle errors in your application in a clean and efficient manner. By understanding how error handling middleware works and how to use it effectively, you can improve the user experience of your application and make it more robust and reliable.