Skip to content
Guide Docs

Process & Signals

Process & Signals

The process object in Node.js is a global object that provides information about, and control over, the current Node.js process. As a global, it is always available to Node.js applications without using require().

1. Environment Variables (process.env)

The process.env property returns an object containing the user environment. It is commonly used to store configuration and secrets.

console.log(process.env.NODE_ENV); // production or development
console.log(process.env.PORT);

2. Command Line Arguments (process.argv)

The process.argv property returns an array containing the command-line arguments passed when the Node.js process was launched.

// Run as: node app.js arg1 arg2
process.argv.forEach((val, index) => {
  console.log(`${index}: ${val}`);
});

3. Process Events & Signals

The process object is an instance of EventEmitter. You can listen for various events or system signals.

Exit Codes

You can exit a process manually using process.exit(code). A code of 0 means success, while non-zero means failure.

if (error) {
  process.exit(1);
}

Handling Signals (SIGINT, SIGTERM)

Signals are sent to the process by the operating system.

  • SIGINT: Sent when you press Ctrl+C in the terminal.
  • SIGTERM: Sent by process managers (like PM2 or Docker) to request a graceful shutdown.
process.on('SIGTERM', () => {
  console.log('SIGTERM received. Cleaning up...');
  // Close database connections, stop server, etc.
  process.exit(0);
});

Uncaught Exceptions & Rejections

It’s crucial to handle errors that escape your normal try/catch blocks.

process.on('uncaughtException', (err) => {
  console.error('There was an uncaught error', err);
  process.exit(1);
});


process.on('unhandledRejection', (reason, promise) => {
  console.error('Unhandled Rejection at:', promise, 'reason:', reason);
  // Application specific logging, throwing an error, or other logic here
});

[!WARNING] Using uncaughtException should be a last resort. It’s often better to let the process crash and have a process manager (like PM2) restart it.