Chechbox checked change event in Updatepanel

var prm = Sys.WebForms.PageRequestManager.getInstance();

    if (prm != null) {

        prm.add_endRequest(function (sender, e) {

            if (sender._postBackSettings.panelsToUpdate != null) {

                callx();

            }

        });

    };

    function callx() {

        $("#<%=chkSaveOnDocLib.ClientID%>").change(function () {

            if (this.checked) {                

                var dt = new Date();

                var time = dt.getHours() + dt.getMinutes() + dt.getSeconds();

               

                document.getElementById("txtFileName").value = document.getElementById("hdnCurrentUser").value + time;

            }

            else {

                document.getElementById("txtFileName").value = "";

            }

        });

    }