node.js - local 方式 npm install 在子目录中重复安装 express

Question

各位兄台，最近刚学 node.js 使用 npm install local 方式安装 遇到软件包重复安装问题：

目录结构：

1. nodejs 主目录：~/code/nodejs/
2. nodejs 子项目：~/code/nodejs/test

主目录 安装 express

gentoo ~/code/nodejs $ npm install express --save
express@4.12.3 node_modules/express
├── merge-descriptors@1.0.0
├── utils-merge@1.0.0
├── cookie-signature@1.0.6
├── methods@1.1.1
├── cookie@0.1.2
├── fresh@0.2.4
├── escape-html@1.0.1
├── range-parser@1.0.2
├── content-type@1.0.1
├── finalhandler@0.3.4
├── vary@1.0.0
├── parseurl@1.3.0
├── serve-static@1.9.2
├── content-disposition@0.5.0
├── path-to-regexp@0.1.3
├── depd@1.0.0
├── qs@2.4.1
├── on-finished@2.2.0 (ee-first@1.1.0)
├── debug@2.1.3 (ms@0.7.0)
├── etag@1.5.1 (crc@3.2.1)
├── send@0.12.2 (destroy@1.0.3, ms@0.7.0, mime@1.3.4)
├── type-is@1.6.1 (media-typer@0.3.0, mime-types@2.0.10)
├── accepts@1.2.5 (negotiator@0.5.1, mime-types@2.0.10)
└── proxy-addr@1.0.7 (forwarded@0.1.0, ipaddr.js@0.1.9)

子目录 安装 express-generator

测试 express-generator 的 子目录 ： ~/code/nodejs/test

gentoo ~/code/nodejs $ mkdir test && cd test

gentoo ~/code/nodejs/test $ npm install express-generator --save
npm WARN prefer global express-generator@4.12.1 should be installed with -g
express-generator@4.12.1 ../node_modules/express-generator
├── sorted-object@1.0.0
├── commander@2.6.0
└── mkdirp@0.5.0 (minimist@0.0.8)

express-generator 是安装在 nodejs 开发 主目录 下的 ~/code/nodejs/node_modules 目录：

gentoo /home/i/code/nodejs 
$ tree -L 2 ~/code/nodejs/node_modules/
/home/i/code/nodejs/node_modules/
├── express
│   ├── History.md
│   ├── index.js
│   ├── lib
│   ├── LICENSE
│   ├── node_modules
│   ├── package.json
│   └── Readme.md
└── express-generator
    ├── bin
    ├── LICENSE
    ├── node_modules
    ├── package.json
    ├── README.md
    └── templates

但发现在 主目录 和 子目录 下的 node_modules 都有安装 express

主目录 的 express 目录树：

主目录 下的 express 目录树，比 子目录 多安装了 debug 包：

gentoo /home/i/code/nodejs
$ tree -L 2 node_modules/express
node_modules/express
├── History.md
├── index.js
├── lib
│   ├── application.js
│   ├── express.js
│   ├── middleware
│   ├── request.js
│   ├── response.js
│   ├── router
│   ├── utils.js
│   └── view.js
├── LICENSE
├── node_modules
│   ├── accepts
│   ├── content-disposition
│   ├── content-type
│   ├── cookie
│   ├── cookie-signature
│   ├── debug                   <--
│   ├── depd
│   ├── escape-html
│   ├── etag
│   ├── finalhandler
│   ├── fresh
│   ├── merge-descriptors
│   ├── methods
│   ├── on-finished
│   ├── parseurl
│   ├── path-to-regexp
│   ├── proxy-addr
│   ├── qs
│   ├── range-parser
│   ├── send
│   ├── serve-static
│   ├── type-is
│   ├── utils-merge
│   └── vary
├── package.json
└── Readme.md

28 directories, 11 files

子目录 的 express 目录树：

gentoo /home/i/code/nodejs/test
$ tree -L 2 node_modules/express/
node_modules/express/
├── History.md
├── index.js
├── lib
│   ├── application.js
│   ├── express.js
│   ├── middleware
│   ├── request.js
│   ├── response.js
│   ├── router
│   ├── utils.js
│   └── view.js
├── LICENSE
├── node_modules
│   ├── accepts
│   ├── content-disposition
│   ├── content-type
│   ├── cookie
│   ├── cookie-signature
│   ├── depd
│   ├── escape-html
│   ├── etag
│   ├── finalhandler
│   ├── fresh
│   ├── merge-descriptors
│   ├── methods
│   ├── on-finished
│   ├── parseurl
│   ├── path-to-regexp
│   ├── proxy-addr
│   ├── qs
│   ├── range-parser
│   ├── send
│   ├── serve-static
│   ├── type-is
│   ├── utils-merge
│   └── vary
├── package.json
└── Readme.md

27 directories, 11 files

WHY

为什么 子目录 不能复用 主目录 的 express 还要 重复安装 呢？

Answer 1

Two questions
1. Regarding express-generator, it is an express project generator of yeoman, as shown in the error reminder npm WARN prefer global express-generator@4.12.1 should be installed with -g. To use it, in addition to
npm install -g yo grunt-cli bower installing the yeoman three-piece set globally, all generated generator (package ending with generator), you must also install npm install -g express-generator globally, and then execute yo express in the directory where you want to create an express project to create a seed project for the opportunity generator. The two express packages you see, one is native to express, and the other is a generator
2. Regarding why nodejs packages cannot be reused.
The modularization of nodejs uses the commonjs specification. When require, it will search for the module under node_modules in the current directory by default. If not, it will search for the node_modules in the parent directory until the root directory. If it does not exist, all projects will be installed in the node directory. Used. What needs to be pointed out here is that the global installation of -g is not globally available. It just generates an executable program placed under the path, such as npm install -g bower, and then you can call the bower program on the command line, such as Any directory bower install jquery
Read more basic things and have a good understanding of node’s module mechanism. I hope my answer will be helpful to you

Answer 2

I still think maven’s version management is better than npm