vue报错：无法启动服务器，报错（npm run dev 报错问题）（一）

vue 项目报错大全（一）
vue报错：无法启动服务器，报错（npm run dev 报错问题）
#出错背景
自己搭建的vue框架，在搭建好一个项目时忽然报错（在此之前其他项目正常运行中，搭建了新的项目启动服务时启动不了了。
#报错代码
Invalid configuration object. webpack-dev-server has been initialised using a configuration object that does not match the API schema.

• configuration.before should be an instance of function
  Exposes the Express server to add custom middleware or routes before webpack-dev-middleware will be added…
  npm ERR! code ELIFECYCLE
  npm ERR! errno 1
  npm ERR! [email protected] start: webpack-dev-server --config config/webpack.dev.js
  npm ERR! Exit status 1
  npm ERR!
  npm ERR! Failed at the [email protected] start script.
  npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
  
  npm ERR! A complete log of this run can be found in:
  #解决方案*
  通过查找发现是因为还没有编写mock文件里的内容（好低级的错误。。）