在ajax應(yīng)用中，通常一個頁面要同時發(fā)送多個請求，如果只有一個XMLHttpRequest對象，前面的請求還未完成，后面的就會把前面的覆蓋掉，如果每次都創(chuàng)建一個新的XMLHttpRequest對象，也會造成浪費。解決的辦法就是創(chuàng)建一個XMLHttpRequset的對象池，如果池里有空閑的對象，則使用此對象，否則將創(chuàng)建一個新的對象。
下面是我最近寫的一個簡單的類：
/**
* XMLHttpRequest Object Pool
*
* @author legend <legendsky@hotmail.com>
* @link http://www.ugia.cn/?p=85
* @Copyright www.ugia.cn
*/
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(fā)送請求(方法[post,get], 地址, 數(shù)據(jù), 回調(diào)函數(shù))
sendReq: function (method, url, data, callback)
{
var objXMLHttp = this._getInstance();
with(objXMLHttp)
{
try
{
// 加隨機數(shù)防止緩存
if (url.indexOf("?") > 0)
{
url += "&randnum=" + Math.random();
}
else
{
url += "?randnum=" + Math.random();
}
open(method, url, true);
// 設(shè)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);
}
}
}
};
* XMLHttpRequest Object Pool
*
* @author legend <legendsky@hotmail.com>
* @link http://www.ugia.cn/?p=85
* @Copyright www.ugia.cn
*/
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(fā)送請求(方法[post,get], 地址, 數(shù)據(jù), 回調(diào)函數(shù))
sendReq: function (method, url, data, callback)
{
var objXMLHttp = this._getInstance();
with(objXMLHttp)
{
try
{
// 加隨機數(shù)防止緩存
if (url.indexOf("?") > 0)
{
url += "&randnum=" + Math.random();
}
else
{
url += "?randnum=" + Math.random();
}
open(method, url, true);
// 設(shè)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);
}
}
}
};
示例：
<script type="text/javascript" src="xmlhttp.js"></script>
<script type="text/javascript">
function test(obj)
{
alert(obj.statusText);
}
XMLHttp.sendReq('GET', 'http://www.ugia.cn/wp-data/test.htm', '', test);
XMLHttp.sendReq('GET', 'http://www.ugia.cn/wp-data/test.htm', '', test);
XMLHttp.sendReq('GET', 'http://www.ugia.cn/wp-data/test.htm', '', test);
XMLHttp.sendReq('GET', 'http://www.ugia.cn/wp-data/test.htm', '', test);
alert('Pool length:' + XMLHttp._objPool.length);
</script>
<script type="text/javascript">
function test(obj)
{
alert(obj.statusText);
}
XMLHttp.sendReq('GET', 'http://www.ugia.cn/wp-data/test.htm', '', test);
XMLHttp.sendReq('GET', 'http://www.ugia.cn/wp-data/test.htm', '', test);
XMLHttp.sendReq('GET', 'http://www.ugia.cn/wp-data/test.htm', '', test);
XMLHttp.sendReq('GET', 'http://www.ugia.cn/wp-data/test.htm', '', test);
alert('Pool length:' + XMLHttp._objPool.length);
</script>
