本地编辑测试,访问http://www.imooc.com/data/check_f.php会产生下面的问题:
Access to XMLHttpRequest at 'http://www.imooc.com/data/check_f.php' from origin 'http://127.0.0.1:5500' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
用IE浏览器打开，不要用谷歌浏览器。