PHP - pasar variable javascript a php

<script type="text/javascript">

function ver_id() {

    if (!document.getElementsByTagName || !document.createTextNode) return;

     var rows = document.getElementById('miTabla').getElementsByTagName('tr');

    for (i = 0; i < rows.length; i++) {

        rows[i].onclick = function() {

		var result = this.getElementsByTagName('td')[1].innerHTML;

            alert(result);

        }

    }

}

</script>

<?php

$producto="<script type='text/javascript'>document.write(result)</script>";

echo "productos=".$producto;

?>

var request = new XMLHttpRequest();

request.open('POST', '/my/url', true);

request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');

request.send('result=' + result);