javascript - 發送請求時，時常在發起前多一條請求，會有哪些原因造成？
介面都是CORS跨域
多出的一條請求：Request Method:OPTIONS、沒有傳遞參數
#多出的條請求的response headers
Access-Control-Allow-Credentials:true
Access-Control-Allow-Headers:Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers
Access-Control-Allow-Methods:POST, GET, PUT, OPTIONS, DELETE
Access-Control-Allow-Origin:*
Access-Control-Max-Age:3600
Allow:GET, HEAD, POST, PUT, DELETE, TRACE, OPTIONS, PATCH
Connection:keep-alive
Content-Length:0
Date:Fri, 05 May 2017 09:27:40 GMT
Server:WildFly/10
X-Powered-By:Undertow/1正常要求的response headers
#Access-Control-Allow-Credentials:true
Access-Control-Allow-Headers:Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers
Access-Control-Allow-Methods:POST, GET, PUT, OPTIONS, DELETE
Access-Control-Allow-Origin:*
Access-Control-Max-Age:3600
Connection:keep-alive
Content-Type:application/json;charset=UTF-8
Date:Fri, 05 May 2017 09:27:41 GMT
Server:WildFly/10
Set-Cookie:JSESSIONID=Zv7WiKxKZFNkE6ihLsGfGwYF8ZEFNEFxENl7rNLW.localhost; path=/bridge
Transfer-Encoding:chunked
X-Powered-By:Undertow/1
