Check if a year is leap year

const isLeapYear = (year) => (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;

// Or
// Get the number of days in February
const isLeapYear = (year) => new Date(year, 1, 29).getDate() === 29;

const isLeapYear = (year: number): boolean => (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;

// Or
const isLeapYear = (year: number): boolean => new Date(year, 1, 29).getDate() === 29;