Comments on: How to know if it’s a leap year

By: Trent Gardner

Trent Gardner — Mon, 26 Jul 2010 10:31:06 +0000

function isLeap(year) {
return (year % 400 == 0 || (year % 100 != 0 && year % 4 == 0));
}

Should be the most efficient way to calculate this.

By: pkang

pkang — Sun, 27 Sep 2009 03:47:53 +0000

here is an article of how to determine a leap year.

http://faq.puthik.com/js/js_faq_leapY.html

By: Dan

Dan — Tue, 28 Apr 2009 18:27:33 +0000

@pam
From the “leap year” article on Wikipedia :
“However, some exceptions to this rule are required since the duration of a solar year is slightly less than 365.25 days. Years that are divisible by 100 are not leap years, unless they are also divisible by 400, in which case they are leap years.”

Take a look at http://en.wikipedia.org/wiki/Leap_year

By: pam

pam — Tue, 28 Apr 2009 18:19:40 +0000

Why do you guys have to make things so complicated? If the last digit of the year ends with a 0,2,4,6, or 8 then its a leap year! It doesn’t take a rocket scientist to figure that one out!

By: dear john

dear john — Fri, 27 Mar 2009 19:21:55 +0000

if you ever forget how to calculate:
http://en.wikipedia.org/wiki/Leap_year

and there is also pseudo-code which can easily be translated to any language.

By: Aunt Edie

Aunt Edie — Fri, 20 Mar 2009 20:32:55 +0000

I like the one from Katatunix–easy to see the date logic and its progression returns a value as quickly as possible. Thanks!

By: Dan

Dan — Thu, 19 Feb 2009 13:04:39 +0000

Why does everyone wants to use the old way with the if and the modulo?

new Date(theYear,1,29).getDate() == 29 is so much better!

By: ALT

ALT — Thu, 19 Feb 2009 02:51:57 +0000

if ( ((year % 4 == 0) && !(year % 100 == 0))
|| (year % 400 == 0) )
numDays = 29;
else
numDays = 28;

By: SANiK

SANiK — Mon, 01 Sep 2008 02:41:10 +0000

Correct code:
var dateObject = new Date(theYear,1,29);
var isLeap = dateObject.getDate() == 29;

To get the # of days in February, one would do:
var dateObject = new Date(theYear,2,0);
var daysInMonth = dateObject.getDate();

“Huh, why is it a ’2′ now?”
Date(2008, 2, 1) is March 1st which is ’1′
Date(2008, 2, 0) is March 0, which doesn’t exist and it would wrap BACK to February =o

By: Dan Simard

Dan Simard — Mon, 10 Dec 2007 21:07:17 +0000

The point was that

new Date(theYear,1,29).getDate() == 29

was the easiest way of doing it. No hard to read parenthesis or special move, just a simple date object creation…