Date validation in javascript is not working properly.

function DateCheck(element, name) {

var dateString1 = (document.getElementById("<%= txtActiveTillDate.ClientID %>").value);
var active = new Date(dateString1).getDate() + "-" + new Date(dateString1).getMonth() + "-" + new Date(dateString1).getFullYear();
var dateString2 = (document.getElementById("<%= txtPublishingDate.ClientID %>").value);
var publishing = new Date(dateString2).getDate() + "-" + new Date(dateString2).getMonth() + "-" + new Date(dateString2).getFullYear();
var todaydate = new Date().getDate() + "-" + new Date().getMonth() + "-" + new Date().getFullYear();
if (active < todaydate) {
alert('Active Till date must be greater than Today date.');
document.getElementById("<%= txtActiveTillDate.ClientID %>").value = "";
return;
}
if (publishing < todaydate) {
alert('Publishing date must be greater or equal to Today date.');
document.getElementById("<%= txtPublishingDate.ClientID %>").value = "";
return;
}
if (publishing >= active) {
alert('Active Till Date cannot be less than Publishing Date.');
document.getElementById("<%= txtActiveTillDate.ClientID %>").value = "";
return;
}
}