PHP variable doorsturen naar Javascript

<?php
$Recordset1 = new WA_MySQLi_RS("Recordset1",$Woma,0);
$Recordset1->setQuery("SELECT id, datum, uur FROM afspraken ORDER BY id ASC");
$Recordset1->execute();
?>

<?php
$wa_startindex = 0;
while(!$Recordset1->atEnd()) {
  $wa_startindex = $Recordset1->Index;
?>
           <tr style="text-align: left">
             <td width="141" class="tabelhoofding" type="hidden"><?php echo($Recordset1->getColumnVal("id")); ?></td>
             <td width="190" class="tabelhoofding"><?php echo($Recordset1->getColumnVal("datum")); ?></td>
			 <td width="128" class="tabelhoofding"><?php echo($Recordset1->getColumnVal("uur")); ?></td>
   			 <td><input name="button" type="button" class="knop" id="button" title="Afspraak maken" onclick="afspraak()" value="Afspraak maken"></td>
             </tr>
           <?php
  $Recordset1->moveNext();
}
$Recordset1->moveFirst(); //return RS to first record
unset($wa_startindex);
unset($wa_repeatcount);
?>

function afspraak()
{
// invullen PHP variable doorgeven aan variable "xid"	
	
window.open("http://www.mijnpagina.be/afspraak_boeken.php?xid="+xid, '_self', false);    
}