ExpressJS Error Handling

ExpressJS Error Handling involves managing errors that occur during the request-response cycle in an Express application.
It allows developers to define middleware functions specifically for handling errors and responding to clients with appropriate error messages.
Error handling in Express.js is crucial for improving the robustness and reliability of web applications.

1. Overview

ExpressJS Error Handling provides a mechanism to catch and process errors that occur during the execution of middleware functions and route handlers.

Error handling middleware functions have four parameters: err, req, res, and next. When an error occurs, Express.js skips regular middleware and route handlers and calls the next error-handling middleware.

2. Example

Here's an example of error handling middleware in Express.js:

// Error handling middleware
app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).send('Something went wrong!');
});

In this example, the error handling middleware function logs the error stack trace and sends a generic error response with status code 500 to the client.

3. Custom Error Handling

Developers can create custom error classes and handlers for different types of errors. For example:

// Custom error class
class CustomError extends Error {
    constructor(message, statusCode) {
        super(message);
        this.statusCode = statusCode;
        this.name = this.constructor.name;
    }
}

// Custom error handler
app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(err.statusCode || 500).send(err.message || 'Something went wrong!');
});

In this example, a custom error class CustomError is defined with a specific status code, and a custom error handler is implemented to handle instances of CustomError.

4. Conclusion

ExpressJS Error Handling is essential for managing errors effectively in Express applications. By defining error handling middleware and custom error classes, developers can ensure robust error handling and provide meaningful error responses to clients.