前端_005_Nodejs

1.Node.js 是js的一个运行环境，从nodejs诞生后js代码不局限于只在浏览器中执行，此外还能再nodejs里写服务端，用js可以前后端全栈开发

2.Node.js不跟浏览器一样默认含有document,window对象，使用时需要引入

npm包管理器

通过package.json文件进行管理前端需要的包，

package-lock.json 会固化当前安装的每个软件包版本，运行npm update会更新该文件

npm分为本地模式和全局模式，一般带-g 都是全局安装

npm常用命令--save 或 -S: 添加到package.json文件的dependencies列表中（默认行为）。--save-dev 或 -D: 添加到package.json文件的devDependencies列表中，表示该包仅用于开发环境。
npm install --save-dev <PACKAGENAME>
--global 或 -g: 全局安装该包，而不是安装在当前项目中。@<版本号>: 安装指定版本的包。
npm install <package-name>@<version>npm init  //初始化
npm install //安装模块
npm run //执行脚本
npm uninsall //卸载模块
npm update //更新模块
npm ls //查看已安装包
npm run <task-name> //执行脚本任务
npm cache clean //清理npm缓存
npm get registry //获得当前使用镜像源
npm config set registry https://registry.npmjs.org/ //修改镜像源
npm root -g //查看全局安装路径

package.json常用属性

{"name": "test-project","version": "1.0.0","description": "A Vue.js project","main": "src/main.js","private": true,"scripts": {"dev": "webpack-dev-server --inline --progress --config build/webpack.dev.conf.js","start": "npm run dev","unit": "jest --config test/unit/jest.conf.js --coverage","test": "npm run unit","lint": "eslint --ext .js,.vue src test/unit","build": "node build/build.js"},"dependencies": {"vue": "^2.5.2"},"devDependencies": {"autoprefixer": "^7.1.2","babel-core": "^6.22.1","babel-eslint": "^8.2.1","babel-helper-vue-jsx-merge-props": "^2.0.3","babel-jest": "^21.0.2","babel-loader": "^7.1.1","babel-plugin-dynamic-import-node": "^1.2.0","babel-plugin-syntax-jsx": "^6.18.0","babel-plugin-transform-es2015-modules-commonjs": "^6.26.0","babel-plugin-transform-runtime": "^6.22.0","babel-plugin-transform-vue-jsx": "^3.5.0","babel-preset-env": "^1.3.2","babel-preset-stage-2": "^6.22.0","chalk": "^2.0.1","copy-webpack-plugin": "^4.0.1","css-loader": "^0.28.0","eslint": "^4.15.0","eslint-config-airbnb-base": "^11.3.0","eslint-friendly-formatter": "^3.0.0","eslint-import-resolver-webpack": "^0.8.3","eslint-loader": "^1.7.1","eslint-plugin-import": "^2.7.0","eslint-plugin-vue": "^4.0.0","extract-text-webpack-plugin": "^3.0.0","file-loader": "^1.1.4","friendly-errors-webpack-plugin": "^1.6.1","html-webpack-plugin": "^2.30.1","jest": "^22.0.4","jest-serializer-vue": "^0.3.0","node-notifier": "^5.1.2","optimize-css-assets-webpack-plugin": "^3.2.0","ora": "^1.2.0","portfinder": "^1.0.13","postcss-import": "^11.0.0","postcss-loader": "^2.0.8","postcss-url": "^7.2.1","rimraf": "^2.6.0","semver": "^5.3.0","shelljs": "^0.7.6","uglifyjs-webpack-plugin": "^1.1.1","url-loader": "^0.5.8","vue-jest": "^1.0.2","vue-loader": "^13.3.0","vue-style-loader": "^3.0.1","vue-template-compiler": "^2.5.2","webpack": "^3.6.0","webpack-bundle-analyzer": "^2.9.0","webpack-dev-server": "^2.9.1","webpack-merge": "^4.1.0"},"engines": {"node": ">= 6.0.0","npm": ">= 3.0.0"},"browserslist": ["> 1%", "last 2 versions", "not ie <= 8"]
}

cjs和mjs

1.mjs是ECMA module，加载ES相关模块， 使用import和export，这个是ES6标准

cjs是node.js独有的模块，commonjs，使用require()加载和module.exports输出

require()是同步加载，后面的代码必须等待这个命令执行完，才会执行。import命令则是异步加载

2.Node.js 遇到.mjs文件，就认为它是 ES6 模块，默认启用严格模式，默认是加载commonjs

.mjs文件总是以 ES6 模块加载，.cjs文件总是以 CommonJS 模块加载，.js文件的加载取决于package.json里面type字段的设置。 {type:“module”}

3.网页中引入使用module 的js 可以指定script 其type 为modules

Ps:
Es模块只能通过http 协议工作，不支持file:// 本地打开文件 所以只能通过搭建服务器的方式打开使用Es 模块的网页

另外不要尝试用vs code里liveserver 插件尝试使用import 或者require 方式，这个插件起的服务器是找不到这种方式引入的模块

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其他nodejs提供许多后端语言支持的特性，如文件操作，异步…等等 这个用到时查找官方手册即可

node.js手册

ackage.json里面type`字段的设置。 {type:“module”}

Yarn包管理器

yarn.lock 锁定依赖包版本

yarn init
yarn install
yarn add [package]
yarn add [package]@[version]
yarn add [package]@[tag]
yarn add [package] --dev  # dev dependencies
yarn add [package] --peer # peer dependencies
yarn up [package]
yarn up [package]@[version]
yarn up [package]@[tag]
yarn remove [package]
yarn config set <name> <value>
yarn config set registry
``