1 // 'month' is starting from 0 2 // daysInMonth(2022, 1) -> 28 3 const daysInMonth = (year, month) => { 4 const dayInMs = 1000 * 60 * 60 * 24; 5 const nextMonthFirstDay = new Date(year, month + 1, 1); 6 7 return new Date(nextMonthFirstDay - dayInMs).getDate(); 8 };