JavaScript: Check whether a given year is a leap year in the Gregorian calendar

function leapyear(year)
{
return (year % 100 === 0) ? (year % 400 === 0) : (year % 4 === 0);
}
console.log(leapyear(2016));
console.log(leapyear(2000));
console.log(leapyear(1700));
console.log(leapyear(1800));
console.log(leapyear(100));

 Output:

true
true
false
false
false