const form = document.querySelector('form');
const formData = new FormData(form);
formData.append('extra', 'value');
console.log(formData.has('extra'), formData instanceof FormData);

async function test() {
  const result = await Promise.resolve(10);
  return result * 2;
}
test().then(value => console.log(value));

:root {
  --spacing: 10px;
}
.box {
  padding: calc(var(--spacing) * 2);
  margin: calc(var(--spacing) / 2);
}

const text = 'apple,banana,cherry';
const arr = text.split(',');
const joined = arr.join(' - ');
console.log(joined);

const arr = [1, 2, 3, 4, 5];
const result = arr.at(-2);
arr.push(6);
console.log(result);

.element {
  position: absolute;
  inset: 20px;
}

const regex = /\d+/g;
const str = 'abc123def456';
console.log(regex.test(str), regex.test(str));

const user = { name: 'Alice' };
const { name, age = 25, city = 'NY' } = user;
console.log(age, city);

.list li:first-of-type {
  color: red;
}
.list li:last-of-type {
  color: blue;
}

const numbers = [5, 10, 15, 20];
const index = numbers.findLastIndex(n => n > 12);
console.log(index, numbers[index]);