Reading and writing files

fs/promises and path

import { readFile, writeFile, mkdir } from "node:fs/promises";
import path from "node:path";

const file = path.join("data", "orders.json");

const orders = JSON.parse(await readFile(file, "utf8"));
orders.push({ id: orders.length + 1, dish: "Momo", qty: 2 });

await mkdir("backup", { recursive: true });
await writeFile(file, JSON.stringify(orders, null, 2));
await writeFile(path.join("backup", "orders.json"), JSON.stringify(orders));

console.log("Saved", orders.length, "orders");
console.log(await readFile(file, "utf8"));

• Missing file? readFile rejects with an error whose code is "ENOENT" — catch it and use a default.
• Relative paths resolve from the folder you started Node in (process.cwd()); in ES modules use import.meta.dirname for the file's own folder.
• Writing JSON files is fine for small tools; real apps use a database (later courses!).