process

JavaScript · Reference cheat sheet

📋 Overview

Node.js exposes the current process as the global process object: environment, CLI args, working directory, exit codes, and stdio streams. Available without an import in most contexts; you can also import process from "node:process".

🔧 Core concepts

• process.env: environment variables (strings or undefined).
• process.argv: [nodePath, scriptPath, ...args].
• process.cwd(): current working directory (not the script’s folder).
• process.exit(code?): end process; 0 success, non-zero failure.
• stdin / stdout / stderr: readable/writable streams for I/O.
• Signals / events: process.on("SIGINT", ...), beforeExit, uncaughtException (use sparingly).

💡 Examples

import process from "node:process";

// CLI: node app.js --port 9000
const args = process.argv.slice(2);
console.log(process.execPath); // node binary
console.log(process.cwd());

const port = process.env.PORT ?? "9000";

process.stdout.write("hello\n");
console.error("to stderr"); // often process.stderr

// Read stdin (piped input)
async function readStdin() {
  const chunks = [];
  for await (const chunk of process.stdin) chunks.push(chunk);
  return Buffer.concat(chunks).toString("utf8");
}

process.on("SIGINT", () => {
  console.log("shutting down…");
  process.exit(0);
});

if (!process.env.REQUIRED) {
  console.error("REQUIRED is missing");
  process.exit(1);
}

// Change cwd (affects relative fs paths)
process.chdir("/tmp");

⚠️ Pitfalls

• process.exit() skips pending I/O and finally cleanup; prefer letting the loop drain or use exitCode = 1.
• cwd() is where you launched the process, not __dirname / import.meta.url.
• argv includes node and script paths — slice from index 2 for user args.
• Mutating process.env affects the current process only (not the parent shell).
• Unhandled promise rejections may terminate Node depending on version/flags.

🔗 Related

• dotenv — load .env into process.env
• Path — resolve paths relative to cwd
• Stream — stdin/stdout as streams
• child_process — spawn subprocesses
• Buffer — binary stdin chunks