Node.js Error Handling - Operational vs Programmer Errors & Production Resilience

A single unhandled exception in Node.js will crash the entire server process, dropping all active user connections across your application. To build enterprise systems with 99.99% uptime, you must master the distinction between Operational Errors and Programmer Errors and implement robust error architecture.

Building a Custom Production AppError Class

Standard JavaScript Error objects lack HTTP status codes and operational flags. Create a reusable domain error class:

// errors/AppError.js
class AppError extends Error {
  constructor(message, statusCode) {
    super(message);
    this.statusCode = statusCode;
    this.status = `${statusCode}`.startsWith('4') ? 'fail' : 'error';
    this.isOperational = true; // Flags this as a known, handled error!

    // Capture clean stack trace omitting this constructor
    Error.captureStackTrace(this, this.constructor);
  }
}

module.exports = AppError;

Process-Level Crash Guards

Configure top-level listeners to catch unexpected errors and restart cleanly:

// server.js - Process-Level Error Handlers
process.on('unhandledRejection', (reason, promise) => {
  console.error('[UNHANDLED REJECTION] Reason:', reason);
  // Close server gracefully and exit
  process.exit(1);
});

process.on('uncaughtException', (err) => {
  console.error('[UNCAUGHT EXCEPTION] Fatal bug encountered:', err);
  // Node.js process state is now corrupt. Must exit!
  process.exit(1);
});