Select one field of many

function selectone(objSource, objArgs) {

var fldvalid;
var first = document.getElementById('<%= flImage.ClientID %>')
var second = document.getElementById('<%=txtembed.ClientID %>')
var third = document.getElementById('<%=FileUpload2.ClientID %>')
if (first.value == "" && second.value == "" && third.value == "") {
fldvalid = false;
}
else if (first.value != "" && second.value != "" && third.value != "") {
fldvalid = false;
}
else if (first.value != "" && second.value != "")
fldvalid = false;
else if (first.value != "" && third.value != "")
fldvalid = false;
else if (second.value != "" && third.value != "")
fldvalid = false;
else {
fldvalid = true;
}
objArgs.IsValid = fldvalid;
return;
}


asp:CustomValidator ID="CustomValidator2" ValidationGroup="News" runat="server"
ClientValidationFunction="selectone" Display="None"
ValidateEmptyText="true" ErrorMessage="Required One video path or embed or image." asp:CustomValidator