Just a simple script which uses maths to detect whether or not a year is a leap year or not. If the year inputted is then "true" will be returned, if not "false".

To use the script just use

leapYear(date);

e.g.

leapYear(2012);

This function can of course be used within any other function e.g.

alert(leapYear(2012));

Remember to put within !!

function leapYear()
{
    var date = new Date();
        date.setFullYear((arguments.length > 0) ? arguments[0] : date.getFullYear());

    var divNumber = ((date.getFullYear() + '').slice(-2) == "00") ? 400 : 4;

    return (date.getFullYear() / divNumber == Math.round(date.getFullYear() / divNumber)) ? true : false;
}