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;
}