调用方法：
<script language = "javascript" src = "count.php"></script>
count.php源码：
<?php
$file_name = "count.txt";
$fp = fopen($file_name,"r"); //打开文件读入当前计数
$count = fread($fp, filesize($file_name));
fclose($fp);
$count++; //计数加1
$fp = fopen($file_name, "w"); //再次打开文件写入更新后的计数
fwrite($fp, $count);
fclose($fp);
echo "document.write('".$count."')"; //输出JavaScript代码，返回计数
?>