onsubmit事件不适用于异步表单提交

我使用struts标签创建了一个表单。我使用struts jquery的submit标签异步提交了表单。在我提交表单之前，我想调用一个javascript函数 checkUser（），检查是否存在客户端错误并阻止表单提交。具有javascript函数的表单如下：

I have created a form using struts tags. I have submitted the form asynchronously using struts jquery's submit tag. Now before i submit my form i want to call a javascript function checkUser() , that checks if there is some client side error And prevents the form from submitting. The form with the javascript function is as follows:

<script type="text/javascript">
    function loadXMLDoc() {

        var xmlhttp;
        var k = document.getElementById("register_userDetails_username").value;

        var urls = "pass.jsp?ver=" + k;

        if (window.XMLHttpRequest) {
            xmlhttp = new XMLHttpRequest();
        } else {
            xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
        xmlhttp.onreadystatechange = function() {
            if (xmlhttp.readyState == 4) {
                document.getElementById("err1").innerHTML = xmlhttp.responseText;
            }
        };
        xmlhttp.open("GET", urls, true);
        xmlhttp.send();
    }
</script>
<script type="text/javascript">
      function checkuser() {
          alert("hi");  
            var i = document.getElementById('err1').innerHTML.search("Unavailable");
            alert(i);
            var j= document.getElementById('err1').innerHTML.search("Min length:8");
            alert(j);
            if (i!= -1 || j!=-1) {
                alert("hello");
                return false;
            } 
            alert("false");
            return false;
      } 

</script>



<%@ taglib prefix="s" uri="/struts-tags"%>
<%@ taglib prefix="sj" uri="/struts-jquery-tags"%>
<jsp:include page="menubar.jsp"></jsp:include>
<s:form action="register" method="post" theme="css_xhtml" cssClass="form1" style="margin:8px 211px" onsubmit="return checkuser()">
    <div class="searchHeader">Sign Up</div>  
    <div id="passwordMatchError">
        <s:property value="error"/>
    </div>
    <s:textfield label="Name" name="userDetails.name" maxlength="30"/>
    <s:textfield label="Username"  name="userDetails.username" onkeyup="loadXMLDoc()" maxlength="30">
        <div id="err1"></div>
    </s:textfield> 
    <s:password label="Password" name="userDetails.password" maxlength="45"/>
    <s:hidden name="userDetails.role" value='U' />
    <s:password name="confirmPassword" label="Confirm Password" maxlength="45"/>
    <s:radio label="Sex" name="userDetails.sex" list="#{'M':'Male','F':'Female'}" />
    <s:textfield label="Phone No" name="userDetails.phoneno" maxlength="10"/>
    <s:textfield label="E-mail" name="userDetails.email" maxlength="45"/>
    <div id="submitdivid"> 
        <sj:submit value="SUBMIT" cssClass="orangebuttonsmall" targets="mainContent" id="sas" />
    </div>
</s:form>

现在，当我在db中已经存在的用户名字段中输入一些值时，它显示字符串不可用在div中，其id为错误。

Now when i enter some value in username field that already exist in db, then it shows string Unavailable in div having id as err.

On onsubmit 表单事件，我调用 checkuser 方法。但是使用 sj：submit ， onsubmit 事件不正在运行。谁能帮助我如何调用make this onsubmit work我的目的是阻止表单提交，如果存在String Unavailable 或最小长度：8 in div err 。任何替代解决方案也被接受。

On onsubmit event of form , I have called checkuser method. But with sj:submit, onsubmit event is not working. Can anyone help me with how to call make this onsubmit work My aim is to prevent form from submitting , if there exists the String Unavailable or Min Length:8 in div err. Any alternative solutions are also accepted.