XMLHttpRequest cannot load http://xxx.cn. Request header field Content-Type is not allowed by Access-Control-Allow-Headers.

解决方法 设置header  PHP设置如下

header('Access-Control-Allow-Origin: *');
header("Access-Control-Allow-Headers: Origin, X-Requested-With, Content-Type, Accept");
header('Access-Control-Allow-Methods: GET, POST, PUT,DELETE');