function isValidDate(dateStr) { var year = Number(dateStr.substr(0,4)); var month = Number(dateStr.substr(4,2)); var day = Number(dateStr.substr(6,2)); if (month < 1 || month > 12) { // check month range alert("Month must be between 1 and 12. "); return false; } if (day < 1 || day > 31) { alert("Day must be between 1 and 31. "); return false; } if ((month==4 || month==6 || month==9 || month==11) && day==31) { alert("Month "+month+" doesn't have 31 days! "); return false } if (month == 2) { // check for february 29th var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)); if (day>29 || (day==29 && !isleap)) { ...