写一个ajax funciton

function Ajax(url)
{
var m_xmlReq=null;
if(window.ActiveXObject)
{
try
{
m_xmlReq = new ActiveXObject('Msxml2.XMLHTTP');
}
catch(e)
{
try{m_xmlReq = new ActiveXObject('Microsoft.XMLHTTP');}catch(e){}
}
}
else if(window.XMLHttpRequest)
{
m_xmlReq = new XMLHttpRequest();
}
this.post=function(d)
{
if(!m_xmlReq) return;
m_xmlReq.open('POST',url,false);
m_xmlReq.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded;charset=utf-8');
m_xmlReq.send(d);
return eval(m_xmlReq.responseText);
}
}