npm源：npm install命令下载需要依赖包的服务器地址，默认是 npm ---- https://registry.npmjs.org/
而国外的源速度太慢，所以我们一般都用国内的淘宝源taobao - https://registry.npm.taobao.org/
我们可以通过nrm工具管理npm的源。
一：安装nrm
npm install -g nrm
二：查看nrm命令帮助文档
nrm -h
Usage: nrm [options] [command] Commands: ls List all the registries current Show current registry name use <registry> Change registry to registry add <registry> <url> [home] Add one custom registry del <registry> Delete one custom registry home <registry> [browser] Open the homepage of registry with optional browser test [registry] Show response time for specific or all registries help Print this help Options: -h, --help output usage information -V, --version output the version number
三：常用命令：
1.nrm ls 查看已有的源
2.nrm add <源名称> <源地址> //新增源
3.nrm use <源名称>. //切换源
