isLeapYear

Checks if the given year is a leap year.

• Use new Date(), setting the date to February 29th of the given year.
• Use Date.prototype.getMonth() to check if the month is equal to 1.

const isLeapYear = year => new Date(year, 1, 29).getMonth() === 1;

isLeapYear(2019); // false
isLeapYear(2020); // true