index.js

<script type="text/javascript">
    // attach the 'textFieldClicked' event
    TXTextControl.addEventListener("textFieldClicked", function (e) {
        fieldClicked(e.fieldName, e.fieldType, e.typeName);
    });

    // do an AJAX postback on the UpdatePanel
    function fieldClicked(fieldName, fieldType, typeName) {
        __doPostBack('<%= UpdatePanel1.ClientID %>', fieldName);
    }
</script>