nodejs express 启动报错:Error: Cannot find module 'xxx'

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

 > [email protected] start D:\nodejs\myapp
 > node ./bin/www

 module.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)

package.json 文件

 {
   "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"
   }
 }

如果你手动在 package.json 文件中添加依赖的话，就需要在你的项目目录（我的目录是：D:\nodejs\myapp）下执行：npm install

还有一个方法是执行：npm install 模块名称 --save

 D:\nodejs\myapp>npm install express-session --save
 [email protected] node_modules\express-session
 ├── [email protected]
 ├── [email protected]
 ├── [email protected]
 ├── [email protected]
 ├── [email protected]
 ├── [email protected]
 ├── [email protected]
 └── [email protected] ([email protected], [email protected])

记得把我这里提到的'xxx'或 'express-session' 替换为你遇到 的错误信息中提示的模块名称哦！