function callback(){
var xmlDoc = this.responseXML;
var root = xmlDoc.
getelementsbytagname('root')[0];
var nodes = root.getElementsByTagName("username");
var
currentNode = null;
var username = document.getElementById('username').value;
for(var i = 0; i < nodes.length;
i++) {
currentNode = nodes[i];
if(username
== currentNode.childNodes[0].nodeValue){
document.getElementById('test').innerHTML = '对不起!'+username+'已经被注册。';
return;
}
}
document.getElementById('test').innerHTML = '用户名' + username +'可以使用!';
}