You need ClientID
in javascript not the server id as asp.net will generate the new CliendID for server controls and the selector you have wont find element by that id.
$("#<%= RdbToday.ClientID %>").change(function () {
$("#dateSelectorSpan").hide();
});
$("#<%= RdbDateRange.ClientID %>").change(function () {
$("#dateSelectorSpan").show();
});
Edit
The code you have is working.
$("#RdbToday").change(function () {
$("#dateSelectorSpan").hide();
});
$("#RdbDateRange").change(function () {
$("#dateSelectorSpan").show();
});
2
solved Change div visibility when radio button becomes selected [closed]