<script type="text/javascript" src="Scripts/jquery-1.4.1.js"></script>

<script type="text/javascript">
$(function () {
$("#txtId").blur(function () {
var a = $("#txtId").val();
$.ajax({
type: "post",
url: "Handler1.ashx",
data: { m: a },
success: function (result) {
var res = result.toString();
$("#lblShow").html(res);
}
});
});
});
</script>

        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";
            string Name = context.Request.Params["m"].ToString();

            if (AdminManager.nameIsExist(Name) == ture)
            {
                context.Response.Write("此用户名已被注册！");
            }
            else
            {
                context.Response.Write("此用户名可以使用！");
            }
        }