JAVASCRIPT 最简单的 AJAX

    //根据不同浏览器创建 httprequest对象 
    function createAjax(){
        if (window.ActiveXObject){
            var iex = new Array("MSXML2.XMLHTTP.5.0","MSXML2.XMLHTTP.4.0","MSXML2.XMLHTTP.3.0","MSXML2.XMLHTTP4","Microsoft.XMLHTTP");
            for (var i = 0;i < iex.length;i++){
                try{
                    var x = new ActiveXObject(iex[i]);
                    return x;
                }
                catch(err){}
            }
            return x;
        }
        
        else if (window.XMLHttpRequest){
            var x = new XMLHttpRequest();
            return x;
        }
    }
            //通过httprequest对象 进行 post 调用
            function GetDbsxCount(sid,amount) {
                xmlHttp = createAjax(); //获取httprequest对象
                var postString = "sid="+sid+"&amount="+amount ; //传递参数
                var url = "commodity_updateAmount.action";
                xmlHttp.open("post", url, false);
                xmlHttp.setRequestHeader ("Content-Type", "application/x-www-form-urlencoded" )
                //xmlHttp.onreadystatechange = callBack_CheckCount;
                xmlHttp.send(postString); //传递参数

            }

            //回调函数，用来接收返回值
            function callBack_CheckCount() {
                if (4 == xmlHttp.readyState) {
                    if(200 == xmlHttp.status)
                    {
                    
                    }
                }
            }