How can I log errors in an Express application?

How can I log errors in an Express application?

You can use middleware to log errors in Express. A common approach is to create an error-handling middleware function.

What should the error-handling middleware look like?

Here's a basic example:

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

Can I log errors to a file instead of the console?

Yes, you can use libraries like winston or morgan to log errors to a file. Would you like an example?

Yes, please provide an example using winston.

Sure! First, install winston:

npm install winston

Then, set it up like this:

const winston = require('winston');

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

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