Node.js

// ESM (modern — use this)
import fs from "node:fs/promises";
import { readFile, writeFile } from "node:fs/promises";
export const greet = name => `Hello, ${name}`;
export default class Server { /* ... */ }

// CommonJS (legacy)
const fs = require("fs");
module.exports = { greet };

// package.json — choose one:
// "type": "module"   → .js files are ESM
// "type": "commonjs" → .js files are CJS (default)
// Use .mjs / .cjs to override per-file

import { readFile, writeFile, mkdir, readdir, stat, unlink } from "node:fs/promises";

// Read file
const content = await readFile("file.txt", "utf8");

// Write file
await writeFile("out.txt", "hello", "utf8");

// Create directory
await mkdir("logs", { recursive: true });

// List directory
const files = await readdir("./src");

// File info
const info = await stat("file.txt");
info.size;         // bytes
info.isDirectory(); // false

// Delete
await unlink("tmp.txt");

import { createServer } from "node:http";

const server = createServer((req, res) => {
  if (req.method === "GET" && req.url === "/health") {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(JSON.stringify({ status: "ok" }));
    return;
  }
  res.writeHead(404);
  res.end("Not Found");
});

server.listen(3000, () => {
  console.log("Server on http://localhost:3000");
});

// Graceful shutdown
process.on("SIGTERM", () => server.close(() => process.exit(0)));

import { EventEmitter } from "node:events";

class JobQueue extends EventEmitter {
  add(job) {
    this.emit("job:added", job);
    this.process(job);
  }
  async process(job) {
    try {
      const result = await job.run();
      this.emit("job:done", { job, result });
    } catch (err) {
      this.emit("job:error", { job, err });
    }
  }
}

const queue = new JobQueue();
queue.on("job:done", ({ job, result }) => console.log(result));
queue.on("error", err => console.error(err)); // Always handle error!