查看当前源：npm config get registry
npm切换源：
切换至淘宝源npm config set registry=http://registry.npm.taobao.org/
切换至华为源npm config set registry=https://mirrors.huaweicloud.com/repository/npm/
切换至npm源npm config set registry=http://registry.npmjs.org
临时使用npm --registry https://registry.npm.taobao.org install express
