如何从Javascript AJAX调用到PHP获取POST值？

Here is the Javascript AJAX code:

var anything=document.getElementById("textarea").val;

I have Javascript AJAX implemented:

httpRequest.open('POST',anyURL,true);
http.send(anything);

Now, my question is since this is the post data, and this is not actually associated with any html tag or id, how do I receive this in php?

<?php 

    $parameter=$_POST['   '];

?>

What should I put in the white space there?

Add a new variable and use JSON.stringify on your anything variable that was turned into a key value pair.

var anything={myTextArea: document.getElementById("textarea").value};
var JSONstr = JSON.stringify(anything);

PHP:

<?php 
    $parameter=$_POST['JSONstr'];
?>