<script type="text/javascript">//页面加载完毕后执行$(document).ready(function(){ ???????//用户名输入框绑定事件 ???????$("#username").focusout(function(){ ???????????//得到输入框的值 ???????????var $text = $("#username").val(); ???????????//光标离开，ajax发送请求 ???????????$.ajax({ ???????????????url:"/test/myServlet", ???????????????type:"post", ???????????????data:{"name":$text}, ???????????????success:function(data){ ???????????????????//data是返回的值，内部通过parse()方法将json字符串转换成json对象 ???????????????????var $info = ""; ???????????????????//获得返回的值 ???????????????????var $exit = data.exit; ???????????????????//判断再显示 ???????????????????if($exit){ ???????????????????????$info="可以使用"; ???????????????????????$("#msg").css("color","green"); ???????????????????}else{ ???????????????????????$info="该用户已存在！"; ???????????????????????$("#msg").css("color","red"); ???????????????????} ???????????????????$("#msg").html($info); ???????????????}, ???????????????error:function(data){ ???????????????????alert("请求错误"); ???????????????}, ???????????????dataType:"json" ???????????}); ???????}); ???????????});</script> <body> 用户名：<input type="text" id="username"> <span id="msg"></span> </body>--------------------- 作者：菜鸟一梦 来源：CSDN 原文：https://blog.csdn.net/m0_37860769/article/details/78984299?utm_source=copy 版权声明：本文为博主原创文章，转载请附上博文链接！服务端代码（用servlet模拟）：
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
//获得输入框输入的值
String name = request.getParameter("name");
boolean b = false;
if(name.equals("123")){
b=true;
}
//以JSON字符串的形式返回
response.getWriter().write("{\"exit\":"+b+"}");
}
ajax实现输入用户名异步提示是否可用
原文地址：https://www.cnblogs.com/waves-a/p/9796881.html