关于cli工具和脚手架的原理（菜鸟前端学习笔记）

问题

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• 什么是脚手架?什么是CLI?
• @vue/cli, create-react-app是如何实现的？

脚手架，CLI

1. 脚手架是一类快速形成工程化目录的工具(业务类型)，如：yeoman, @vue/cli, create-react-app.
2. CLI(command-line-interface, 缩写：CLI)(效率工具)， 如：webpack, es-lint, json-server

平常开发中经常会用到如上熟悉的脚手架，cli工具，那么这些工具，工具是如何实现的呢？原理是什么呢？

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git源码浏览

• 以@vue/cli为例，通过npmjs,github找到源码。
• package.json中，查找dependencies, 程序入口
• 浏览@vue/cli的代码工程化结构

话不多说，按照咱们的想法，先去github，vue/cli的工程上，瞅一瞅源码。对着package.json一阵观看:

 "devDependencies": {
    "@babel/core": "^7.9.0",
    "@vue/eslint-config-airbnb": "^5.0.2",
    "@vue/eslint-config-prettier": "^6.0.0",
    "@vue/eslint-config-standard": "^5.1.2",
    "@vue/eslint-config-typescript": "^5.0.2",
    "@vuepress/plugin-pwa": "^1.4.0",
    "@vuepress/theme-vue": "^1.4.0",
    "@typescript-eslint/eslint-plugin": "^2.26.0",
    "@typescript-eslint/parser": "^2.26.0",
    "babel-core": "7.0.0-bridge.0",
    "babel-eslint": "^10.1.0",
    "babel-jest": "^24.9.0",
    "chromedriver": "^80.0.1",
    "debug": "^4.1.0",
    "eslint": "^6.7.2",
    "eslint-plugin-import": "^2.20.2",
    "eslint-plugin-graphql": "^3.1.0",
    "eslint-plugin-node": "^11.1.0",
    "eslint-plugin-prettier": "^3.1.1",
    "eslint-plugin-promise": "^4.2.1",
    "eslint-plugin-standard": "^4.0.0",
    "eslint-plugin-vue": "^6.2.2",
    "eslint-plugin-vue-libs": "^4.0.0",
    "execa": "^1.0.0",
    "geckodriver": "^1.19.1",
    "globby": "^9.2.0",
    "graphql": "^14.6.0",
    "http-server": "^0.12.1",
    "inquirer": "^7.1.0",
    "jest": "^24.9.0",
    "lerna": "^3.19.0",
    "lerna-changelog": "^0.8.3",
    "lint-staged": "^9.5.0",
    "memfs": "^3.1.2",
    "minimist": "^1.2.5",
    "prettier": ">= 1.13.0",
    "request": "^2.88.2",
    "request-promise-native": "^1.0.8",
    "rimraf": "^3.0.2",
    "semver": "^6.1.0",
    "typescript": "~3.8.3",
    "vuepress": "^1.3.0",
    "webpack": "^4.0.0",
    "yorkie": "^2.0.0"
  },

嗯，里面有许多我们平常写项目也会经常用到的依赖，不过也有些我一点都不认识的，当对这些不熟悉的依赖中有几个典型的可以介绍一下，比如：execa，inquirer，vuepress。

• execa:是一个js操作shell的工具，是很好的子进程管理工具；
• inquirer: 是一个用户与命令行交互的工具，例如，我们在使用@vue/cli创建项目的时候，会有一些选择配置的交互，大概就是用这个实现的；
• vuepress: 适用于发布项目的技术文档，静态网页生成器

当然这些都不是vue/cli整个项目的部分依赖，我们再去找找，项目的入口文件，我们点到项目的packages目录中，会看到一堆目录，找到我们的cli文件夹，点进去，看看package.json瞅瞅；

{
  "name": "@vue/cli",
  "version": "4.3.1",
  "description": "Command line interface for rapid Vue.js development",
  "bin": {
    "vue": "bin/vue.js"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/vuejs/vue-cli.git",
    "directory": "packages/@vue/cli"
  },
  "keywords": [
    "vue",
    "cli"
  ],
  "author": "Evan You",
  "license": "MIT",
  "bugs": {
    "url": "https://github.com/vuejs/vue-cli/issues"
  },
  "homepage": "https://cli.vuejs.org/",
  "publishConfig": {
    "access": "public"
  },
  "dependencies": {
    "@vue/cli-shared-utils": "^4.3.1",
    "@vue/cli-ui": "^4.3.1",
    "@vue/cli-ui-addon-webpack": "^4.3.1",
    "@vue/cli-ui-addon-widgets": "^4.3.1",
    "boxen": "^4.1.0",
    "cmd-shim": "^3.0.3",
    "commander": "^2.20.0",
    "debug": "^4.1.0",
    "deepmerge": "^4.2.2",
    "download-git-repo": "^3.0.2",
    "ejs": "^2.7.1",
    "envinfo": "^7.5.0",
    "fs-extra": "^7.0.1",
    "globby": "^9.2.0",
    "import-global": "^0.1.0",
    "inquirer": "^7.1.0",
    "isbinaryfile": "^4.0.5",
    "javascript-stringify": "^1.6.0",
    "js-yaml": "^3.13.1",
    "jscodeshift": "^0.7.0",
    "leven": "^3.1.0",
    "lodash.clonedeep": "^4.5.0",
    "lru-cache": "^5.1.1",
    "minimist": "^1.2.5",
    "recast": "^0.18.8",
    "resolve": "^1.15.1",
    "shortid": "^2.2.15",
    "slash": "^3.0.0",
    "validate-npm-package-name": "^3.0.0",
    "vue": "^2.6.11",
    "vue-jscodeshift-adapter": "^2.0.2",
    "yaml-front-matter": "^3.4.1"
  },
  "engines": {
    "node": ">=8.9"
  }
}

可以看到项目的入口文件是bin目录下的vue.js,稍后我们进去瞅瞅，看看用到的这些依赖，发现了一个commander, 具体的用处可以点开链接去看看。总而言之，就是node.js命令行接口的解决工具。最后，咱去看看vue.js,代码就不贴了，利用一系列的依赖来实现了用户与命令行的整个交互流程，还有一些复杂项目包管理配置操作，最终实现了脚手架快速创建项目的过程。

总结原理

• commander获取用户传参
• inquirer与用户进行交互，获取用户输入选项
• bin执行文件，cli命令的入口。

后续会跟随学习，进一步更新学习的笔记，最终实现一个简易的脚手架工具。