<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<input type="button" value="请求" id="btn">
<script type="text/javascript">
var oBtn=document.getElementById('btn');
oBtn.onclick=function(){
//1 创建一个请求
if (window.XMLHttpRequest) {
//chrome safari forefox ie7+
var httpRequest = new XMLHttpRequest();
} else {
//IE6
var httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
}
//2 连接服务器
// httpRequest.open(发送方式(get/post),url请求的地址，true异步-默认/false-同步)
httpRequest.open('GET', 'a.txt');
//3 发送请求
httpRequest.send();
//4 接受结果
httpRequest.onreadystatechange = function() {
if (httpRequest.readyState == 4) {
if (httpRequest.status === 200) {
//请求过来的东西，放到 re...Text
console.log(httpRequest.responseText);
//把input的value变成我请求的文字
oBtn.value = httpRequest.responseText;
//已经完成
} else {
//有一个有问题的请求
// 404-页面没有找到 或 500 服务器错误
}
}
}
}
</script>
</body>
</html>
