Set the javascript parameter to a hidden field.
Access the hidden field from your code behind.
JavaScript:
<script>
function SendValueToCodeBehind(myValue){
document.getElementById('hdnJavaScriptValue').value = myValue;
}
</script>
ASPX:
<asp:hiddenfield id="hdnJavaScriptValue" runat="server" xmlns:asp="#unknown"></asp:hiddenfield>
Code Behind:
Dim oJavaScriptValue as Object = hdnJavaScriptValue.Value