'vue-cli-service' 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-element-admin@4.2.1 dev: `vue-cli-service serve`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the vue-element-admin@4.2.1 dev 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:
npm ERR!     D:\Program Files\nodejs\node_cache\_logs\2019-10-23T11_18_53_372Z-debug.log
 

解决办法：

打开idea下方 Terminal 窗口输入 npm install --global vue-cli ，下载安装即可。