封装ajax

function ajaxRequest(method,url,sync,param,responseFun){
    //创建对象
    var httpRequest;
    if(window.XMLHttpRequest){

        httpRequest= new XMLHttpRequest();
    }else if(Window.ActiveXObject){
        httpRequest=  new ActiveXObject("Microsoft.XMLHTTP");
    }
    // 回调函数
    httpRequest.onreadystatechange=function(){
        if(httpRequest.readyState==4 && httpRequest.status==200) {
            responseFun(httpRequest.responseText);
        }
    };
    //发起请求
    httpRequest.open(method,url,sync);
    if(method=="post"){
        httpRequest.setRequestHeader("Content-type","application/x-www-form-urlencoded");
    }
    //发送数据到服务器
    httpRequest.send(param);

}