當我們開發一個庫的時候，不可能每次都去釋出到npm或者私服，然後再去應用中安裝。所以，無論npm或者 yarn都提供了link命令用以簡化開發流程。

以yarn為例，首先進入到庫的根目錄中，執行yarn link，值得注意的時候，當前目錄顯然應該有package.json檔案，且應包含釋出的名稱和入口檔案。

此時相當於將當前包釋出到了全域性環境，這個時候，對應的應用就可以通過yarn link @scope/your-lib命令新增該包。其實僅僅是建立了一個軟連線，即一個快捷方式。

至此就成功繞過了發包的流程，而且得益於僅僅是一個建立一個軟連線，使得每次重新構建庫之後，應用可以立即看到效果，從而實現快速的本地開發。

yarn官網原文 地址：https://yarn.bootcss.com/docs/cli/link/

Symlink a package folder during development.

For development, a package can be linked into another project. This is often useful to test out new features or when trying to debug an issue in a package that manifests itself in another project.

There are two commands to facilitate this workflow:

yarn link(in package you want to link)

This command is run in the package folder you’d like to consume. For example if you are working onreactand would like to use your local version to debug a problem inreact-relay, simply runyarn linkinside of thereactproject.

yarn link [package...]

Useyarn link [package]

Complete example, assuming two project foldersreactandreact-relaynext to each other:

$ cd react
$ yarn link
yarn link vx.x.x
success Registered "react".
info You can now run `yarn link "react"` in the projects where you want to use this module and it will be used instead.

$ cd ../react-relay
$ yarn link react
yarn link vx.x.x
success Registered "react".

This will create a symlink namedreact-relay/node_modules/reactthat links to your local copy of thereactproject.

Links are registered in~/.config/yarn/link. If you want to specify a different folder you can run the command with this syntaxyarn link --link-folder path/to/dir/