提示这样的错误：Uncaught TypeError: Cannot read property 'getElementsByTagName' of null
alert明明有输出却还是显示这样的错误，ballball各位大佬教教我！！！
<div class="form-group">
<div class="label">
<label>工号：</label>
</div>
<div class="field">
<input type="text" style="width:25%; float:left;"
class="input w50" value="" name="userid" id ="userid" onblur="validate()"
data-validate="required:请输入工号" />
<div id="usermsg"></div>
</div>
</div>
<script type="text/javascript">
var req;
function validate() {
var idField = document.getElementById("userid");
var url = "${pageContext.request.contextPath}/page/user/validate.jsp?id="
+ escape(idField.value);
// alert(url);
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
} else if (window.ActiveXObject) {
req = new ActiveXObject("Microsoft.XMLHTTP");
}
req.open("GET", url, true);
req.onreadystatechange = callback;
req.send(null);
}
function callback() {
if (req.readyState == 4) {
if (req.status == 200) {
alert(req.responseText);
var msg = req.responseXML.getElementsByTagName("msg")[0];
// alert(msg);
setMsg(msg.childNodes[0].nodeValue);
}
}
}
function setMsg(msg) {
// alert(msg);
mdiv = document.getElementById("usermsg");
if (msg == "invalid") {
mdiv.innerHTML = "<font color='red'>username exists</font>";
} else {
mdiv.innerHTML = "<font color='green'>congratulations! you can use this username!</font>";
}
}
</script>
validate.jsp
<body>
<%
response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-store"); //HTTP1.1
response.setHeader("Pragma", "no-cache"); //HTTP1.0
response.setDateHeader("Expires", 0); //prevents catching at proxy server
response.setHeader("Cache-Control", "no-cache");
System.out.println(request.getParameter("id"));
String userid = request.getParameter("id");
System.out.println(userid);
User u = new User();
boolean userExist = u.CheckUserid(userid);
System.out.println(userExist);
if (userExist) {
response.getWriter().write("<msg>invalid</msg>");
} else {
response.getWriter().write("<msg>valid</msg>");
}
%>
</body>
慕粉1755528293回答
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相关分类
JavaScript