url-一个php文件向另一个php文件传变量，$_POST取不

index.php里：
var request = new XMLHttpRequest();
request.open("POST","test.php");
request.setRequestHeader("Content-type","application/x-www-form-urlencoded");
var str="name="+url;
request.send(str);

text.php里：
$url=$_POST['name'];
echo $url;
两个文件在同一工程下，url是个变量,text.php执行会提示undefined index:name
readyState=4 Status=0 ,请问哪儿出错了