cart_js/cart.jsの一番最後の行の
window.onload=Cart;
の下に

function Send(act,data,u){

var xhr=new XMLHttpRequest();

xhr.onreadystatechange = function(){
switch(xhr.readyState){
case 0:
break;
case 1:
break;
case 2:
break;
case 3:
break;
case 4:
if(xhr.status == 200 || xhr.status == 304) {
var txt=xhr.responseText;
var s=txt.substr(0,3);

if(s == "ok:" || s == "er:"){
var tmp=txt.split(":");
if(tmp[0] == "ok"){
ShowData(act,tmp[2],tmp[3]);
}
else{
var msg_ob_tmp=GetMsgOb(act);
var msg_ob=msg_ob_tmp[0];
var ob_tmp=GetOb(act);
var ob=ob_tmp[0];
MsgErr(msg_ob,tmp[1]);
ObErr(ob);
}
}
else{
var msg_ob_tmp=GetMsgOb(act);
var msg_ob=msg_ob_tmp[0];
var ob_tmp=GetOb(act);
var ob=ob_tmp[0];
MsgErr(msg_ob,"エラーが発生しました");
ObErr(ob);
}

}
break;
}
}

xhr.open("POST",u);
xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
xhr.send( EncodeHTMLForm(data));
}

function EncodeHTMLForm(data){
var params=[];
for(var name in data){
var value=data[name];
var param=encodeURIComponent(name)+'='+encodeURIComponent(value);
params.push(param);
}
return params.join('&').replace(/%20/g,'+');