let obj = { a: 1, b: { c: 2 } };
let clone = structuredClone(obj);
clone.b.c = 99;
console.log(obj.b.c); // 2

document.addEventListener("visibilitychange", () => {
  if(document.hidden) console.log("کاربر رفت");
  else console.log("کاربر برگشت");
});

// worker.js
self.onmessage = e => {
  let result = e.data * 2;
  postMessage(result);
};

// main.js
let worker = new Worker('worker.js');
worker.postMessage(5);
worker.onmessage = e => console.log(e.data); // 10

fetch('/bigfile.txt')
  .then(res => res.body.getReader())
  .then(reader => reader.read().then(console.log));

let buffer = new SharedArrayBuffer(1024);
let arr = new Int32Array(buffer);
arr[0] = 42;

let bc = new BroadcastChannel('channel_name');
bc.onmessage = e => console.log(e.data);
bc.postMessage('سلام از تب دیگه!');

let user = {};
console.log(user?.address?.city); // undefined (بدون ارور)