监听 dom 改变

function jt() {
            //显示
            var zw = document.getElementById('s2id_txtCounterName');
            if (zw == null) {
                setTimeout(function () { jt(); }, 30);
                return;
            }
            var zwtxt = zw.getElementsByClassName("select2-chosen"); //设置职务名称

            //监听内容改变事件

            zwtxt[0].addEventListener("DOMSubtreeModified", function (evt) {
                var zgxm = document.getElementById("showUserPicker2");
                zgxm.innerText = '';
                zgxm.setAttribute("val", '');
            }, false);

        }