Here you can find the source of isLeapYear(year)
Date.isLeapYear = function (year) { return (((year % 4 === 0) && (year % 100 !== 0)) || (year % 400 === 0)); };
Date.prototype.isLeapYear = function () { var year = this.getFullYear(); return ((year & 3) == 0 && (year % 100 || (year % 400 == 0 && year)));
Date.prototype.isLeapYear = function () { return new Date(this.getFullYear(), 1, 29).getDate() == 29; };
Date.prototype.isLeapYear = function() { return Date.isLeapYear(this.getFullYear()); };
Date.prototype.isLeapYear = function () var y = this.getFullYear(); return (((y % 4 === 0) && (y % 100 !== 0)) || (y % 400 === 0)); };
Date.isLeapYear = function(year) { return (((year % 4 === 0) && (year % 100 !== 0)) || (year % 400 === 0)); };
function { return year%4==0&&(year%100!=0||year%400==0);