怎样从 Javascript 传递一个变量到 PHP

<?php
if (isset($_GET['width']) AND isset($_GET['height'])) {
  // output the geometry variables
  echo"Screen width is: ".$_GET['width'] ."<br />\n";
  echo"Screen height is: ".$_GET['height'] ."<br />\n";
} else {
  // pass the geometry variables
  // (preserve the original query string
  //   -- post variables will need to handled differently)

  echo"<scrīpt language='javascrīpt'>\n";
  echo"  location.href=\"${_SERVER['scrīpt_NAME']}?${_SERVER['QUERY_STRING']}"
            ."&width=\" + screen.width + \"&height=\" + screen.height;\n";
  echo"</scrīpt>\n";
  exit();
}
?>

PS:(流行的网站流量统计方式才有此方法)