ajax演示Created by IntelliJ IDEA.To change this template use F

周末有小伙伴问到我ajax问题，我做了个小小的DEMO来演示一下啊：

首先，我们做一个简单的也页面，做一个表单

<%--
  Created by IntelliJ IDEA.
  User: bo
  Date: 2020/4/12
  Time: 17:04
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>注册</title>
    <script src="js/jquery-3.3.1.min.js"></script>


    <script>
        $(function () {

            $("#username").blur(function () {
                var username = $(this).val();
                $.post("findUserServlet",{"username":username},function (data) {
                   // alert(data.userExsit);
                    var span = $("#myspan");
                    if(data.userExsit){ // 判断
                        span.css("color","red");