var httpRequest=null;
function createXHR(){		
	if(window.XMLHttpRequest) { //Mozilla 浏览器
      httpRequest = new XMLHttpRequest();
      if (httpRequest.overrideMimeType) {//设置MiME类别
         httpRequest.overrideMimeType("text/xml");
      }
    }
    else if (window.ActiveXObject) { // IE浏览器
      try {httpRequest = new ActiveXObject("Msxml2.XMLHTTP");}
      catch (e)
      {
        try {httpRequest = new ActiveXObject("Microsoft.XMLHTTP");}catch (e) {}
      }
    }
    if (!httpRequest) { // 异常，创建对象实例失败
      window.alert("不能创建XMLHttpRequest对象实例.");
    }
} 

function sendRequest(url,params,method,handler){
	createXHR();
	if(!httpRequest) return false;	
	httpRequest.onreadystatechange = handler;
	httpRequest.open(method,url+ '?' + params,true);
	if(method == "GET"){		
		httpRequest.send(null);
	}
	if(method == "POST"){
		httpRequest.setRequestHeader("Content-type","application/x-www-form-urlencoded");
		httpRequest.send(params); 
	}
}