Question

I do not usually use JavaScript, and cannot see why this is not working. Thanks.

function testYear() {
    var dObject = new Date();
    var dRegEx = /^[0-9][0-9]00$/;
    var d = dObject.getFullYear();

    if (d.match(dRegEx) && d % 400 == 0) {
    alert("The year "+d+" is in fact a leap year!");
    //return true;
    }
    else if(!(d.match(dRegEx) && d % 400) && d % 4 == 0) {
    alert("The year "+d+" is in fact a leap year!");
    //return true;
    }
    else {
    alert("The year "+d+" is not a leap year.");
    //return false;
    }
}

Answer 1

There’s no need to use a regular expression here. Just use an ordinary integer arithmetic to see if the year is divisible by 100:

if (d % 100 === 0 && ...)

By the way, if d % 400 === 0 then it is automatically true that d % 100 === 0 so the extra test is unnecessary.

---

A year is a leap year in the Gregorian calendar either if it is divisible by 400 or if it is divisible by 4, but not by 100. Try this instead:

if ((d % 400 === 0) || (d % 4 === 0 && d % 100 !== 0))
{
    // is leap year
}