Ajax緩存問題的解決:Ajax的本質就是將狀態保存在客戶端，因此資源的緩存和再利用是他的優勢所在，但有時候不希望被緩存，例如計數器，不同請求的計數器得到的結果應該是最新的。在線時長也應該每次刷新不一樣。
1)設置隨機數: Math.random();
url: "user.php?username="+username+"&num="+Math.random();
2)設置時間戳
var dateTime = new Date().getTime()
url: "user.php?username="+username+"&num="+dateTime;
3)使用POST代替GET方式提交數據: POST本身提交和返回的數據的不緩存;
4)設置響應頭信息
header("Cache-Control:no-cache");
POST方式數據傳遞:
1、在send前 設置post發送的數據按照URL地址方式傳遞
ajax.setRequestHeader("content-Type","application/x-www-form-urlencoded");
2、open函數中第二個參數只剩下提交地址
3、將傳遞的數據: 參數名=值&參數名=值&...的方式放入到send函數()中
ajax.open("POST","./user.php",false);
//發送
ajax.setRequestHeader("content-TYPE","application/x-www-form-urlencoded");
var data = "uname="+uname;
ajax.send(data);
reg.html
<!DOCTYPE HTML>
<html>
<head>
<title> ajax </title>
<meta charset="utf-8"/>
<script type="text/javascript">
var httpAjax = new XMLHttpRequest();
function checkUser(uname){
if(uname == ""){
return false;
}
httpAjax.onreadystatechange = function(){
if(httpAjax.readyState == 4 && httpAjax.status == 200){
var res = httpAjax.responseText;
var sp = document.getElementById("sp");
if(res == "true"){
sp.innerHTML = "<font color='red'>已註冊</font>";
}else{
sp.innerHTML = "<font color='green'>可以註冊</font>"
}
}
}
httpAjax.open("post","user.php",true);
httpAjax.setRequestHeader("content-TYPE","application/x-www-form-urlencoded");
var data = "uname="+uname; //user.php?uname="1"&pwd="123","uname=" 是參數,+是參數連接變量的用的，uname是js中的一個不帶$的變量，也就是值
httpAjax.send(data);
}
</script>
</head>
<body>
<input type="text" id="username" class="username" name="username" onchange="checkUser(this.value)"/><span id="sp"></span>
</body>
</html>user.php
<?php
header("content-type:text/html;charset=utf-8");
$pdo = new PDO("mysql:host=localhost;dbname=tk106","root","");
$pdo->exec("set names utf8");
$uname = $_REQUEST["uname"];//post傳值，這裏要改爲REQUEST接收
$sql = "select * from stu_info where sname='".$uname."'";
$data = $pdo->query($sql)->fetch(PDO::FETCH_ASSOC);
if($data){
echo "true";
}else{
echo "false";
}
?>