'webpack-dev-server' 不是内部或外部命令，也不是可运行的程序

npm run dev 报错

'webpack-dev-server' 不是内部或外部命令，也不是可运行的程序
或批处理文件。
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! vue-mall@1.0.0 dev: `webpack-dev-server --inline --progress --config build/webpack.dev.conf.js`npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the vue-mall@1.0.0 dev script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm WARN Local package.json exists, but node_modules missing, did you mean to install?
npm ERR! A complete log of this run can be found in:npm ERR!     C:\Users\XXX\AppData\Roaming\npm-cache\_logs\2018-06-20T02_00_23_340Z-debug.log

解决方法:

要先安装扩展 要先安装扩展 要先安装扩展

npm install