process — Process

The Node.js process object — argv, env, exit, stdin/stdout, signals, and working directory.

What it is, in plain English: The process object in Node.js is a global that provides information about and control over the current Node.js process. process.argv holds command-line arguments. process.env holds environment variables. process.exit() terminates the process. process.stdin and process.stdout are streams for reading and writing to the terminal. process.on('SIGINT') lets you handle Ctrl+C gracefully.

Reading args, environment, and controlling the process

Command-line arguments

// process.argv = ["node", "/path/to/script.js", ...user_args]
// node hello.js Alice 42

const [, , name, age] = process.argv;
console.log(`Hello ${name}, you are ${age} years old`);

// Parse --flag value style args:
function parseArgs() {
  const args = {};
  const argv = process.argv.slice(2);  // skip "node" and script path

  for (let i = 0; i < argv.length; i++) {
    if (argv[i].startsWith("--")) {
      const key   = argv[i].slice(2);
      const next  = argv[i + 1];
      args[key]   = next && !next.startsWith("--") ? argv[++i] : true;
    }
  }
  return args;
}

// node server.js --port 8080 --debug
const { port = "3000", debug = false } = parseArgs();
console.log(`Starting on port ${port}, debug: ${debug}`);

Environment variables

// process.env contains all environment variables:
const dbUrl    = process.env.DATABASE_URL;
const apiKey   = process.env.API_KEY;
const nodeEnv  = process.env.NODE_ENV ?? "development";
const isProd   = nodeEnv === "production";

if (!dbUrl) {
  console.error("Missing DATABASE_URL environment variable");
  process.exit(1);  // non-zero exit = error
}

// Load .env file with dotenv package (npm install dotenv):
// import "dotenv/config";  // at the top of your entry file
// Now process.env.MY_VAR works from .env file

Exit codes and signals

// Graceful shutdown:
process.on("SIGTERM", async () => {
  console.log("SIGTERM received — shutting down gracefully");
  await server.close();
  await db.disconnect();
  process.exit(0);  // 0 = success
});

// Ctrl+C:
process.on("SIGINT", () => {
  console.log("
Interrupted — bye!");
  process.exit(0);
});

// Catch unhandled errors (last resort — fix the root cause instead):
process.on("uncaughtException", (err) => {
  console.error("Uncaught:", err);
  process.exit(1);  // 1 = error
});

process.on("unhandledRejection", (reason) => {
  console.error("Unhandled rejection:", reason);
  process.exit(1);
});

Try It Yourself

// process — Node.js global process object
// Available globally in Node.js (no import needed)

// ─── COMMAND LINE ARGS ───────────────────────────────────────────────────────
// process.argv = ["node", "script.js", ...your args]
// node app.js --port 3000 --debug
console.log("argv:", process.argv);

// e.g. node app.js --port 3000 --debug
// parseArgs() → { port: "3000", debug: true }
console.log("Parsed args:", parseArgs(["--port", "3000", "--debug"]));

// ─── ENVIRONMENT VARIABLES ───────────────────────────────────────────────────
console.log("NODE_ENV:", process.env.NODE_ENV ?? "development");
console.log("HOME:", process.env.HOME ?? "N/A");

// Safe env reading with defaults:
const PORT = parseInt(process.env.PORT ?? "3000", 10);
const HOST = process.env.HOST ?? "localhost";
console.log(\`Server would run on \${HOST}:\${PORT}\`);

// ─── PROCESS INFO ────────────────────────────────────────────────────────────
console.log("PID:", process.pid);
console.log("Platform:", process.platform);  // "linux", "darwin", "win32"
console.log("Node version:", process.version);
console.log("Architecture:", process.arch);   // "x64", "arm64"
console.log("CWD:", process.cwd());

// ─── MEMORY ──────────────────────────────────────────────────────────────────
const mem = process.memoryUsage();
console.log("Heap used:", (mem.heapUsed / 1e6).toFixed(1), "MB");
console.log("Heap total:", (mem.heapTotal / 1e6).toFixed(1), "MB");
console.log("RSS:", (mem.rss / 1e6).toFixed(1), "MB");

// ─── EXIT ─────────────────────────────────────────────────────────────────────
// process.exit(0);   // success
// process.exit(1);   // error (non-zero = failure — important for CI/CD!)

stdin/stdout, nextTick, and process.hrtime

// process.stdin — read from terminal:
process.stdin.setEncoding("utf-8");
process.stdin.on("data", (input) => {
  const line = input.trim();
  process.stdout.write(`You typed: ${line}
`);
});

// For scripting — read all of stdin and process:
async function readStdin() {
  const chunks = [];
  for await (const chunk of process.stdin) chunks.push(chunk);
  return Buffer.concat(chunks).toString("utf-8");
}

// process.stdout.write — no newline added (unlike console.log):
process.stdout.write("Loading");
for (let i = 0; i < 3; i++) {
  await new Promise(r => setTimeout(r, 500));
  process.stdout.write(".");
}
process.stdout.write("
");

// process.nextTick — run before any I/O in next iteration:
console.log("sync 1");
process.nextTick(() => console.log("nextTick"));
Promise.resolve().then(() => console.log("Promise.then"));
console.log("sync 2");
// Order: sync 1 → sync 2 → nextTick → Promise.then

// High-resolution timing:
const start = process.hrtime.bigint();  // nanoseconds
doWork();
const elapsed = process.hrtime.bigint() - start;
console.log(`${elapsed / 1_000_000n}ms`);

Process isolation, Worker threads, and spec

// process.memoryUsage() — full breakdown:
const { rss, heapTotal, heapUsed, external, arrayBuffers } = process.memoryUsage();
// rss           — Resident Set Size: total memory allocated for the process
// heapTotal     — total V8 heap size
// heapUsed      — V8 heap actually in use
// external      — C++ objects bound to JS (Buffers)
// arrayBuffers  — memory allocated for ArrayBuffer and SharedArrayBuffer

// process.cpuUsage() — CPU time:
const cpu = process.cpuUsage();
// { user: microseconds, system: microseconds }

// process.resourceUsage() — detailed OS resource usage:
const ru = process.resourceUsage();
// { userCPUTime, systemCPUTime, maxRSS, sharedMemorySize, ... }

// Worker threads vs child processes (process isolation):
// Worker threads: same process, shared memory, lightweight
// child_process.fork: separate process, message-passing, full isolation
// cluster: multiple server processes, automatic port sharing

Official Sources

The Codex links only to official documentation and the ECMAScript specification. No third-party tutorials.