const data = { one: { first: 'first of object', second: 'second' }, two: { third: 'third', quattro: 'quattro' } }; let { one: { first } } = data ; let a = 'two'; data[a].third = 'none'; console.log(data); console.log('first:', first); let arr = [1, 2]; arr.length = 0; console.log(arr);