Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

注意:throw err; // Rethrow non-MySQL errors
虽然报了这个问题,但是并不是数据库链接失败,这种问题的出现是由于,node每次只能返回一次res.send(),如果返回多次就会报这样的错。

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client