window.document.onkeydown = function (evt) {
                         
                        evt = (evt) ? evt : window.event;
                        if (evt.keyCode) {
                            if (evt.keyCode == 9) {//tab
                                $(‘#<%=this.txtCheckCode.ClientID%>‘).val(getCookie(d));
                            }
                        }
                    }

function getCookie(c_name) {
                    if (document.cookie.length > 0) {
                        c_start = document.cookie.indexOf(c_name + "=")
                        if (c_start != -1) {
                            c_start = c_start + c_name.length + 1
                            c_end = document.cookie.indexOf(";", c_start)
                            if (c_end == -1) c_end = document.cookie.length
                            return unescape(document.cookie.substring(c_start, c_end))
                        }
                    }
                    return ""
                }