npm 和 yarn 安装依赖（包）时不会自动安装 peer dependence（虽然很旧的 npm 是会自动安装的，但几乎没人用那么旧的了），而是给出如下警告：
bash
$ npm install --save-dev rollup-plugin-typescript
npm WARN [email protected] requires a peer of tslib@* but none is installed. You must install peer dependencies yourself.
npm WARN [email protected] requires a peer of typescript@>=2.1.0 but none is installed. You must install peer dependencies yourself.
$ yarn add -D rollup-plugin-typescript
yarn add v1.13.0
[1/4] Resolving packages...
[2/4] Fetching packages...
[3/4] Linking dependencies...
warning " > [email protected]" has unmet peer dependency "tslib@*".
warning " > [email protected]" has unmet peer dependency "typescrip
t@>=2.1.0".
并且也没有自动安装 peer dependence 选项，这也就是为什么我们安装某些依赖时需要同时安装多个依赖（包），例如：npm install --save-dev rollup-plugin-typescript typescript tslib。
参考：