完美兼容IE、FF、Opera的Ajax类支持get、post、自定义回调函数

function Ajax(){  

this.httpXML=false;  

this.init();  

}  

Ajax.prototype.init=function(){  

if(window.XMLHttpRequest){  

this.httpXML=new XMLHttpRequest();   

if (this.httpXML.overrideMimeType){  

this.httpXML.overrideMimeType("text/xml");   

}  

}else if(window.ActiveXObject){  

try{this.httpXML = new ActiveXObject("Msxml2.XMLHTTP");}catch (e){   

try{this.httpXML = new ActiveXObject("Microsoft.XMLHTTP");}catch (e){}   

}  

}  

if(!this.httpXML){  

window.alert("can't create XMLHttpRequest object");  

return null;  

}  

}  

Ajax.prototype.send=function(_method,_url,_data,_callback){  

this.httpXML.onreadystatechange=function(){  

if(this.readyState==4&&this.status==200){  

_callback.call(this,this.responseText);  

}  

}      

if (_method.toLowerCase() == "get"){   

this.httpXML.open(_method, _url, true);   

this.httpXML.send(null);   

}else if (_method.toLowerCase() == "post"){   

this.httpXML.open(_method, _url, true);   

this.httpXML.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");   

this.httpXML.send(_data);   

}      

}

//===========================================

function getResult(data){

alert(data);

}

new Ajax().send('post','url','a=1&b=2',getResult);