完整錯誤提示：
錯誤分析：這句警告意思是module文件夾中沒有express框架相關依賴包。
解決方案：只需要運行命令自行安裝express依賴包即可。
PS D:\WEB前端\案例\前端工程化：ES6模塊化和webpack打包\webpack_study> npm install express npm WARN webpack_study@1.0.0 No description npm WARN webpack_study@1.0.0 No repository field. + express@4.17.1 added 50 packages from 37 contributors in 2.751s
成功運行：
PS D:\WEB前端\案例\前端工程化：ES6模塊化和webpack打包\webpack_study> nodemon .\app.js [nodemon] 2.0.7 [nodemon] to restart at any time, enter `rs` [nodemon] watching path(s): *.* [nodemon] watching extensions: js,mjs,json [nodemon] starting `node .\app.js` 服務器連接！