my Solution
function checkdate() {
var InpDate = document.getElementById("<%=txtBirthdate.ClientID%>").value;
var returnval = true;
if (InpDate != '' && InpDate != "__/__/____") {
var monthfield = InpDate.split("/")[0];
var dayfield = InpDate.split("/")[1];
var yearfield = InpDate.split("/")[2];
var dayobj = new Date(yearfield, monthfield - 1, dayfield);
if ((isNaN(dayobj.getMonth() + 1) == true) || (isNaN(dayobj.getDate()) == true) || (isNaN(dayobj.getFullYear())) == true) {
returnval = false;
}
if (yearfield < 1900) {
returnval = false;
}
if (dayobj.getDate() != dayfield) {
returnval = false;
}
if (dayobj.getMonth() + 1 != monthfield) {
returnval = false;
}
}
return returnval
}