const obj1 = { a: 1, b: 2 };
const obj2 = { b: 3, c: 4 };
const merged = { ...obj1, ...obj2 };
console.log(merged.b, Object.keys(merged).length);

.parent {
  font-size: 16px;
}
.child {
  font-size: 2rem;
  margin: 1em;
}

const arr = [10, 20, 30, 40, 50];
const sliced = arr.slice(1, -1);
console.log(sliced);

const value1 = null ?? 'default';
const value2 = 0 ?? 'default';
const value3 = '' ?? 'default';
console.log(value1, value2, value3);

@supports (display: grid) {
  .container {
    display: grid;
  }
}
@supports not (display: grid) {
  .container {
    display: flex;
  }
}

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);