Convert javascript date to php date

convert javascript date to php date

function convert_date($date)
    {
        //original date format=yy-mm-dd
        list($d, $m, $y) = split('[/.-]', $date);    
        $new_date=$y.'/'.$m.'/'.$d;    
        return $new_date;
    }

//panggil funcinnya
$start_date='20/1/2013'
$start_date = convert_date($start_date);

hasilnya :
2013/1/20