vue中npm install安装依赖包 --save，–save-dev，-S，-D的区别；先介绍package.json里面的dependencies模块和devDependencies的区别；

1，dependencies和devDependencies的区别：

**dependencies**是生产时的依赖：比如：vue， axios，echarts，element-ui，vant等这些项目打包后也依旧就能够用到的重要依赖；

**devDependencies**是开发时的依赖：比如：eslint，prettier代码美化和检查，sass-loader css预编译，babel es6转es5，uglifyjs-webpack-plugin js代码压缩，image-webpack-loader 图片压缩 等这些
loder , plugin， babel, webpack类的辅助开发或只在打包阶段使用的；不会再生产中使用的依赖我们要放在devDependencies模块里面；

 "dependencies": {
    "axios": "^0.19.0",
    "core-js": "^3.6.5",
    "echarts": "^5.3.3",
    "element-ui": "2.12.0",
    "html2canvas": "1.0.0-rc.7",
    "qrcodejs2": "^0.0.2",
    "recorder-core": "1.1.21021500",
    "vant": "^2.12.8",
    "vconsole": "^3.14.6",
    "vue": "^2.6.11",
    "vue-cli-plugin-mock": "^1.0.3",
    "vue-router": "^3.2.0",
    "vuex": "^3.4.0",
    "vuex-persistedstate": "^4.1.0",
    "xgplayer": "^2.31.6"
  },
  "devDependencies": {
    "@vue/cli-plugin-babel": "~4.5.0",
    "@vue/cli-plugin-eslint": "~4.5.0",
    "@vue/cli-plugin-router": "~4.5.0",
    "@vue/cli-plugin-vuex": "~4.5.0",
    "@vue/cli-service": "~4.5.0",
    "@vue/eslint-config-prettier": "^6.0.0",
    "babel-eslint": "^10.1.0",
    "babel-plugin-component": "^1.1.1",
    "babel-plugin-import": "^1.13.3",
    "eslint": "^6.7.2",
    "uglifyjs-webpack-plugin": "^2.2.0",
    "eslint-plugin-prettier": "^3.3.1",
    "eslint-plugin-vue": "^6.2.2",
    "image-webpack-loader": "^8.1.0",
    "node-sass": "^4.14.1",
    "prettier": "^2.2.1",
    "sass-loader": "^8.0.2",
    "vue-template-compiler": "^2.6.11"
  }

2，–save，–save-dev，-S，-D 这些命令的区别：

• --save 等同于-S（是前者的缩写）：安装包信息将放入到dependencies（生产阶段的依赖,是项目运行时的依赖，程序上线后仍然需要依赖）

使用如下：

  npm install --save  axios
  npm install -S  axios@0.19.0
  加上@0.19.0 是指定版本号；不指定npm默认安装最新的版本；

• –save-dev等价 于-D（也是前者的缩写）：安装包信息将放入到devDependencies（开发阶段的依赖，是我们在开发过程中需要的依赖）

使用如下：

 npm install --save-dev uglifyjs-webpack-plugin
 npm install -D uglifyjs-webpack-plugin