建立一個 XMLHttpRequest 對象池 (附自帶測試檔)


在ajax應用中,通常一個頁面要同時發送多個請求,如果只有一個XMLHttpRequest對象,前面的請求還未完成,後面的就會把前面的覆蓋掉,如果每次都創建一個新的XMLHttpRequest對象,也會造成浪費。解決的辦法就是創建一個XMLHttpRequset的對象池,如果池裡有空閒的對象,則使用此對象,否則將創建一個新的對象。

ajax.js :

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var XMLHttp = {
_objPool: [],

_getInstance: function (){
for (var i = 0; i < this._objPool.length; i ++){
if (this._objPool[i].readyState == 0 || this._objPool[i].readyState == 4){
return this._objPool[i];
}
}
// IE5 中不支持 Push 方法
this._objPool[this._objPool.length] = this._createObj();
return this._objPool[this._objPool.length - 1];
},

_createObj: function (){
if (window.XMLHttpRequest){
var objXMLHttp = new XMLHttpRequest();
}else{
var MSXML = ['MSXML2.XMLHTTP.5.0', 'MSXML2.XMLHTTP.4.0', 'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP', 'Microsoft.XMLHTTP'];
for(var n=0; n<MSXML.length; n++){
try{
var objXMLHttp = new ActiveXObject(MSXML[n]);
break;
}catch(e){}
}
}
// Mozilla 某些版本沒有 readyState 屬性
if (objXMLHttp.readyState == null){
objXMLHttp.readyState = 0;
objXMLHttp.addEventListener("load", function (){
objXMLHttp.readyState = 4;
if(typeof objXMLHttp.onreadystatechange == "function"){objXMLHttp.onreadystatechange();}
}, false);
}
return objXMLHttp;
},

// 發送請求(方法[POST,GET], 地址, 數據, 回調函數)
sendReq: function (method, url, data, callback){
var objXMLHttp = this._getInstance();
with(objXMLHttp){
try{
// 加隨機數防止緩存
if (url.indexOf("?") > 0){url += "&randnum=" + Math.random();}
else{url += "?randnum=" + Math.random();}
open(method, url, true);
// 設定請求編碼方式
setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
send(data);
onreadystatechange = function (){
if (objXMLHttp.readyState == 4 && (objXMLHttp.status == 200 || objXMLHttp.status == 304)){
callback(objXMLHttp);
}
}
}catch(e){alert(e);}
}
}
};

index.html :

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title> new document </title>
<meta http-equiv="Pragma" content="no-cache" />
<meta http-equiv="Expires" content="-1" />
<meta http-equiv="Cache-Control" content="no-cache" />
<link rel="stylesheet" type="text/css" media="screen" href="" />
<script src="ajax.js" language="javascript" type="text/javascript"></script>
<script language="javascript" type="text/javascript">
function $(id) {
return document.getElementById(id);
}
function showInfo(obj) {
$('pageDiv').innerHTML = obj.responseText;
}
function getAjax(url) {
XMLHttp.sendReq('GET', url, null, showInfo);
}
</script>
</head>
<body>
<a href="#" onclick="getAjax('info.html')">個人資料</a>
<hr size="0" />
<div id="pageDiv"></div>
</body>
</html>

info.html

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title> new document </title>
<meta http-equiv="Pragma" content="no-cache" />
<meta http-equiv="Expires" content="-1" />
<meta http-equiv="Cache-Control" content="no-cache" />
<link rel="stylesheet" type="text/css" media="screen" href="" />
<script src="" language="javascript" type="text/javascript"></script>
</head>
<body>
<div id="t">This is my info page</div>
</body>
</html>

相關的資料 : http://www.ugia.cn/?p=85 (作者)