nodejs express 启动报错:Error: Cannot find module 'xxx'，这是因为缺少模块的引用。

比如我在代码中使用了'express-session'，但是却没有在 package.json 文件的 "dependencies" 项中添加 'express-session' 的依赖

D:\nodejs\myapp>set DEBUG=myapp & npm start> myapp@0.0.0 start D:\nodejs\myapp> node ./bin/wwwmodule.js:340    throw err;    ^Error: Cannot find module 'express-session'    at Function.Module._resolveFilename (module.js:338:15)    at Function.Module._load (module.js:289:25)    at Module.require (module.js:366:17)    at require (module.js:385:17)    at Object.
     
       (D:\nodejs\myapp\app.js:6:15)    at Module._compile (module.js:435:26)    at Object.Module._extensions..js (module.js:442:10)    at Module.load (module.js:356:32)    at Function.Module._load (module.js:313:12)    at Module.require (module.js:366:17)
     

{  "name": "myapp",  "version": "0.0.0",  "private": true,  "scripts": {    "start": "node ./bin/www"  },  "dependencies": {    "body-parser": "~1.15.2",    "cookie-parser": "~1.4.3",    "debug": "~2.2.0",    "ejs": "^2.5.5",    "express": "~4.14.0",    "express-session": "^1.14.2",    "mongoose": "^4.7.6",    "morgan": "~1.7.0",    "serve-favicon": "~2.3.0"  }}

还有一个方法是执行：npm install 模块名称 --save

D:\nodejs\myapp>npm install express-session --saveexpress-session@1.14.2 node_modules\express-session├── on-headers@1.0.1├── cookie-signature@1.0.6├── utils-merge@1.0.0├── cookie@0.3.1├── parseurl@1.3.1├── depd@1.1.0├── crc@3.4.1└── uid-safe@2.1.3 (base64-url@1.3.3, random-bytes@1.0.0)

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