var x = 1;      // Function-scoped (avoid)
let y = 2;      // Block-scoped, reassignable
const z = 3;    // Block-scoped, constant

// Destructuring
const { name, age } = obj;
const [a, b] = arr;

// Declaration
function fn() {}
// Expression
const fn = function() {};
// Arrow
const fn = () => {};
// Default params
function fn(a = 1) {}
// Rest params
function fn(...args) {}

arr.map(x => x * 2);
arr.filter(x => x > 2);
arr.reduce((a, b) => a + b, 0);
arr.find(x => x === 2);
arr.some(x => x > 2);
arr.every(x => x > 0);
arr.includes(2);
arr.flat();
arr.sort((a, b) => a - b);

const p = new Promise((res, rej) => {});
p.then(v => {}).catch(e => {}).finally(() => {});

// Async/await
async function fn() {
  try { const r = await fetch(url); }
  catch (e) { console.error(e); }
}

// Promise combinators
Promise.all([p1, p2]);
Promise.race([p1, p2]);
Promise.allSettled([p1, p2]);
Promise.any([p1, p2]);

const obj = { name, age };          // Shorthand
const obj = { [key]: value };       // Computed
const copy = { ...obj };            // Spread
const { name, ...rest } = obj;      // Rest
Object.freeze(obj);
Object.seal(obj);
Object.keys(obj);
Object.values(obj);
Object.entries(obj);

document.querySelector('.class');
document.querySelectorAll('div');
el.textContent = 'text';
el.classList.add('active');
el.addEventListener('click', fn);
el.closest('.parent');
el.remove();