ajax

<script type="text/javascript">

window.onload = function(){

var oBtn = document.getElementById('btn');

var oInp = document.getElementsByTagName('input')[0];

var oBox = document.getElementById('box');

oBtn.onclick = function(){

// 发ajax请求

// 1.创建XMLHttpRequest对象

var req = new XMLHttpRequest();

// 2.打开服务器连接 method url

req.open('get','${pageContext.request.contextPath}/reg_2?uname='+oInp.value,true);

// 3.发送请求

req.send();

// 4.调用回调函数获取响应信息

req.onload = function(){

if(req.responseText == 1){

oBox.innerHTML = '用户名已经注册';

oBox.style.color = 'red';

}else if(req.responseText == 0){

oBox.innerHTML = '用户名可以注册';

oBox.style.color = 'green';

}

}

}

}

</script>