项目启动 npm run dev运行报错

PS D:\VSCODE\express-demo> npm run dev//跟着视频的步骤报错

npm ERR! missing script: dev

npm ERR! A complete log of this run can be found in:

npm ERR!     D:\nodejs\node_cache\_logs\2021-04-13T06_09_30_179Z-debug.log

PS D:\VSCODE\express-demo> npm start//使用之前的启动方法报错

> express-demo@1.0.0 start D:\VSCODE\express-demo

> nodemon ./src/app.js

'nodemon' 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! express-demo@1.0.0 start: `nodemon ./src/app.js`

npm ERR! Exit status 1

npm ERR!

npm ERR! Failed at the express-demo@1.0.0 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:

npm ERR!     D:\nodejs\node_cache\_logs\2021-04-13T06_09_39_374Z-debug.log