Check date in JavaScript

Try this:

if ((myDate.getMonth()+1!=month)||(myDate.getDate()!=day)||(myDate.getFullYear()!=year))
    alert("Date Invalid.");

if ((myDate.getDate() != day) || 
    (myDate.getMonth() != month - 1) || 
    (myDate.getFullYear() != year))
{
    return false;
}

JavaScript just converts entered in Date constructor month, year, day, etc.. in simple int value (milliseconds) and then formats it to represent in string format. You can create new Date(2011, 100, 100) and everythig will ok :)