asp.net XMLHttpRequest实现用户注册前的验证

测试通过环境vs2008，添加2个新项
1：demo3.aspx

//查询字符串,send服务端的参数
function createquerystring() {
var username = document.getelementbyid("username").value;
var querystring = "username=" + username;
return querystring;
}
function runajax() {
//参考'摘自书中有意义的示例中demo1.html如何创建xmlhttprequest对象 代码'
createxmlhttprequest();
var querystring = "ishaveuser.ashx?";
querystring = querystring + createquerystring()
+ "&timestamp=" + new date().gettime();//url上追加时间戳，防止浏览器缓存
xmlhttp.onreadystatechange = handlestatechange;
xmlhttp.open("get", querystring, true);
xmlhttp.send(null);
document.getelementbyid('validatemessage').innertext = '正在检查,请稍候...';
}
function handlestatechange() {
if (xmlhttp.readystate == 4) {
if (xmlhttp.status == 200) {
var result = xmlhttp.responsetext;
document.getelementbyid("validatemessage").innertext = result;
if (result== "恭喜!可以注册...") {
settimeout("document.getelementbyid('validatemessage').innertext='';", 2000);
}
}
}
}
<input id="username" /><input id="ishaveuser" type="button" value="检查用户是否被注册" onclick="runajax();"/><span id="validatemessage" ></span>

2：ishaveuser处理程序

public class ishaveuser : ihttphandler {
public void processrequest (httpcontext context) {
system.threading.thread.sleep(2000);
string username = context.request.querystring["username"];
bool result = 读取数据库执行判断用户名是否存在操作，返回布尔值，省略代码
if (result)
{
context.response.write("恭喜!可以注册...");
}
else { context.response.write("此用户存在,请更换..."); }
}
public bool isreusable { get { return false;}}
}