How can I implement error handling middleware in Express?

How can I implement error handling middleware in Express?

To implement error handling middleware in Express, you can create a middleware function that takes four arguments: err, req, res, and next. Here's a basic example:

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

This middleware will catch any errors that occur in your application and respond with a 500 status code.

Can I customize the error response?

Yes, you can customize the error response by modifying the response object. For example:

app.use((err, req, res, next) => {
    res.status(err.status || 500);
    res.json({
        error: {
            message: err.message,
            status: err.status
        }
    });
});

What if I want to log errors to a file?

You can use a logging library like winston or morgan to log errors to a file. Here's a simple example using winston:

const winston = require('winston');

const logger = winston.createLogger({
    transports: [
        new winston.transports.File({ filename: 'error.log' })
    ]
});

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

Is there a way to handle 404 errors specifically?

Yes, you can create a separate middleware for handling 404 errors. Place it after your routes:

app.use((req, res, next) => {
    res.status(404).send('Sorry, we cannot find that!');
});