JavaScript:
Writing to standard error

How to:

In Node.js, writing to stderr can be accomplished using the console.error() method or by writing directly to process.stderr. Here are examples demonstrating both approaches:

// Using console.error()
console.error('This is an error message.');

// Directly writing to process.stderr
process.stderr.write('This is another error message.\n');

Sample output for both methods would appear in the stderr stream, not mingling with stdout:

This is an error message.
This is another error message.

For more sophisticated or application-specific logging, many JavaScript programmers use third-party libraries like winston or bunyan. Here’s a quick example using winston:

First, install winston via npm:

npm install winston

Then, configure winston to log errors to stderr:

const winston = require('winston');

const logger = winston.createLogger({
  levels: winston.config.syslog.levels,
  transports: [
    new winston.transports.Console({
      stderrLevels: ['error']
    })
  ]
});

// Logging an error message
logger.error('Error logged through winston.');

This setup ensures that when you log an error using winston, it directs to stderr, helping maintain clear separation between standard and error outputs.