javascript如何获取后台数据（JavaScript实现异步获取表单数据）

 <li class="container">
       <form class="form-horizontal" onsubmit="return false;">
           <li class="form-group">
               <label class="control-label col-md-3">姓名：</label>
               <li class="col-md-4">
                   <input type="type" name="txtname" value=" "  class="form-control" id="txtName"/>
               </li>
           </li>
           <li class="form-group">
               <label class="control-label col-md-3">性别：</label>
               <li class="col-md-4">
                   <select class="form-control" name="cboSex" id="cboSex">
                       <option>--请选择</option>
                       <option>男</option>
                       <option>女</option>
                   </select>
               </li>
           </li>
           <li class=" form-group">
               <label class="control-label col-md-3">地址：</label>
               <li class="col-md-4">
                   <textarea class="form-control" name="txtAddress" id="txtAddress"></textarea>
               </li>
           </li>
           <li class="form-group">
               <button class="btn btn-primary col-md-offset-4" onclick="getVal()">获取表单的值</button>
               <button class="btn btn-primary" onclick="postgetData()">提交数据</button>
               <button class="btn btn-success" onclick="getData()">获取数据</button>
           </li>
       </form>
</li>

 function getData() {
            var xhr;
            if (window.XMLHttpRequest) {
                xhr = new XMLHttpRequest();
            } else {
                xhr = ActiveXObject("microsoft.XMLHTTP");
            }
            xhr.open("post", "/JQuery/getInformation", true);
            xhr.send();
            xhr.onreadystatechange = function () {
                if (xhr.status == 200 && xhr.readyState == 4) {
                    var txt = xhr.responseText;//获取xhr的返回值
                    var obj = JSON.parse(txt);//将字符串解析为js对象
                    document.getElementById("txtName").value = obj.name;
                    document.getElementById("cboSex").value = obj.sex;
                    document.getElementById("txtAddress").value = obj.address;
                }
            }
        }

var xhr=new XMLHttpRequest();

var xhr=new ActiveXObject("Microsoft.XMLHTTP");

var xhr;
     if (window.XMLHttpRequest) {
                  // code for IE7+, Firefox, Chrome, Opera, Safari
                    xhr = new XMLHttpRequest();
                } else {
                    // code for IE6, IE5
                    xhr = new ActiveXObject("Microsoft.XMLHTTP");
                }

public ActionResult getInformation()
        {
            string str = "{\"name\":\"三三\",\"sex\":\"男\",\"address\":\"上海市南城区\"}";
            return Content(str);
        }