在被访问的PHP页面头部加入以下代码，即可实现允许JS跨域访问。
<?php
header("access-control-allow-headers: Accept,Authorization,Cache-Control,Content-Type,DNT,If-Modified-Since,Keep-Alive,Origin,User-Agent,X-Mx-ReqToken,X-Requested-With");
header("access-control-allow-methods: GET");//GET, POST, PUT, DELETE, HEAD, OPTIONS
header("access-control-allow-credentials: true");
header("access-control-allow-origin: *");
header('X-Powered-By: WAF/2.0');