OS module

JavaScript · Reference cheat sheet

📋 Overview

Node.js node:os reports host operating system details: home/temp directories, platform, CPU info, memory, and network interfaces. Useful for tools, diagnostics, and default paths — not a substitute for feature detection in app logic.

import os from "node:os";

🔧 Core concepts

• homedir(): current user’s home directory.
• tmpdir(): default directory for temporary files.
• platform(): 'darwin' | 'linux' | 'win32' | … (Node’s naming).
• type() / release() / arch(): OS name, version string, CPU arch (x64, arm64).
• cpus(): array of CPU core descriptors (model, speed, times).
• totalmem() / freemem(): RAM in bytes.
• hostname() / networkInterfaces(): machine name and NICs.
• EOL: end-of-line sequence (\n or \r\n).

💡 Examples

import os from "node:os";
import path from "node:path";

const configDir = path.join(os.homedir(), ".myapp");
const scratch = path.join(os.tmpdir(), "myapp-cache");

console.log(os.platform(), os.arch(), os.release());
console.log("cores:", os.cpus().length);
console.log("free MB:", Math.round(os.freemem() / 1024 / 1024));

const cpus = os.cpus();
console.log(cpus[0]?.model);

// Cross-platform line join
const lines = ["a", "b", "c"].join(os.EOL);

const ifaces = os.networkInterfaces();
for (const [name, addrs] of Object.entries(ifaces)) {
  for (const a of addrs ?? []) {
    if (a.family === "IPv4" && !a.internal) {
      console.log(name, a.address);
    }
  }
}

⚠️ Pitfalls

• platform() returns 'win32' even on 64-bit Windows.
• cpus().length is logical cores (HT), not necessarily physical packages.
• tmpdir() / homedir() can throw or be unexpected in restricted containers.
• networkInterfaces() shape varies; filter internal and family carefully (IPv4 vs 4 in older Node).
• Do not hardcode separators — combine with path and os.EOL.

🔗 Related

• Path — join home/tmp with filenames
• process — env, cwd, platform via process
• fs — create dirs under homedir/tmpdir
• child_process — OS-specific binaries