<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title></title>
<meta charset="utf-8" />
</head>
<body>
<input type="text" id="txt1" value="1212" />
<script>
var obj = document.getElementById('txt1');
console.log(obj.value);
var xmlHttp;
if (window.XMLHttpRequest) {
xmlHttp = new XMLHttpRequest();
} else {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlHttp.onreadystatechange = function () {
if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
console.log(1);
obj.value = xmlHttp.responseText;
}
};
xmlHttp.open('get', 'json1.json', true); // true 异步 false 同步 url: aaa.asp?a=1&b=2
xmlHttp.send(); //send('11111'). 当post的时候提交 '11111'
console.log(2);
//xmlhttp.open("POST", "ajax_test.asp", true);
//xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
//xmlhttp.send("fname=Bill&lname=Gates");
//当为true，打出顺序为 2 1
//当为false，打出顺序为 1 2
</script>
</body>
</html>
教程地址：http://www.w3school.com.cn/ajax/index.asp