当我单击提交按钮时，http 请求从客户端发送到服务器两次。 第一个是 OPTIONS，另一个是 POST 方法。
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HTTP 请求
最佳答案
Preflighted requests
Unlike simple requests (discussed above), "preflighted" requests first send an HTTP OPTIONS request header to the resource on the other domain, in order to determine whether the actual request is safe to send. Cross-site requests are preflighted like this since they may have implications to user data. In particular, a request is preflighted if:
It uses methods other than GET or POST. Also, if POST is used to send request data with a Content-Type other than application/x-www-form-urlencoded, multipart/form-data, or text/plain, e.g. if the POST request sends an XML payload to the server using application/xml or text/xml, then the request is preflighted. It sets custom headers in the request (e.g. the request uses a header such as X-PINGOTHER)
关于html - 为什么http请求从客户端发送到服务器两次(OPTION和POST)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39034178/