使用webpack-dev-server进行ajax时报错。

Question

错误信息：
控制台报错：

Failed to load resource: the server responded with a status of 504 (Gateway Timeout)

CMD报错：

 Error occurred while trying to proxy request /api/json.json from localhost:8080 to http://localhost:9000 (ECONNREFUSED) (https://nodejs.org/api/errors.html#errors_common_system_errors)