Question

<button onclick="isleap(1992)">Try it</button>​

function isleap(year);
{
var yr=document.getElementById("year").value;
if ((parseInt(yr)%4) == 0)
{
 if (parseInt(yr)%100 == 0)
 {
 if (parseInt(yr)%400 != 0)
 {
 alert("Not Leap");
 return "false";
 }
  if (parseInt(yr)%400 == 0)
  {
  alert("Leap");
    return "true";
    }
  }
  if (parseInt(yr)%100 != 0)
  {
    alert("Leap");
    return "true";
  }
 }
 if ((parseInt(yr)%4) != 0)
 {
    alert("Not Leap");
    return "false";
 } 
}

​

http://jsfiddle.net/kcyCd/

Having problems figuring out how to get the code to popup the alert box with the answer to the leap year.

Answer 1

A simple isLeapYear function is:

function isLeapYear(year) {
  var d = new Date(year, 1, 29);
  return d.getMonth() == 1;
}

It just sees if 29 February occurs in the given year. You should be able to do:

function isLeapYear2(year) {
  return !!Date.parse(year + '-02-29');
}

on the basis that parsing an invalid date should return NaN, which type-converts to false, but not all browsers correctly implement Date.parse. e.g.

isLeapYear2('2001'); // false in Firefox, true in IE