ajax传值给php文件问题

[木偶人]

 var concrete = document.getElementById("s6").value;
var xhr = new XMLHttpRequest();
    xhr.onreadystatechange =function(){
        if(xhr.readyState == 4){
            if(xhr.responseText!=false){
                //document.getElementById("newaddress").className="hide";
                //alert(xhr.responseText);
                document.getElementById("introduce").innerHTML=xhr.responseText;
            }
        }
    }
    xhr.open('post',test+"/newaddress");
    xhr.send(concrete);

路径是正确的是http://localhost:8080/mooc/shop/index.php/home/Order/newaddress
怎么在php文件接收不到值啊？？？
求大神解答

[xuzuning]

因为缺少了 xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");