html js上传一直 http请求报错，求指教

Question

Request header field If-Modified-Since is not allowed by Access-Control-Allow-Headers in preflight response.服务端已经设置了Access-Control-Allow-Origin:* ，这个大概会是什么方面的问题呢求指教如何解决啊

Answer 1

从这里看就是跨域问题
header("Access-Control-Allow-Origin:来源域名");
header("Access-Control-Allow-Credentials:true");