2 - 安装

从 Yarn 1 迁移

我们一直在编纂迁移指南为从 Yarn 1 迁移到 Yarn 2 提供有用的建议。请查看此指南，如果发现尚未涵盖的内容请反馈！如果遇到问题，请查阅 PnP 兼容列表和开启 node-modules 插件！

全局安装

Using a single package manager across your system has always been a problem. To be stable, installs need to be run with the same package manager version across environments, otherwise there's a risk we introduce accidental breaking changes between versions - after all, that's why the concept of lockfile was introduced in the first place! And with Yarn being in a sense your very first project dependency, it should make sense to "lock it" as well. 在整个系统中使用单个包管理器一直是个问题。为了稳定，安装需要跨环境使用相同的包管理器版本运行，否则我们有可能在版本之间引入意外中断更改 - 毕竟，这就是为什么首先引入了锁文件的概念！在某种意义上，Yarn 是您的第一个项目依赖项，因此"锁定它"也是有道理的。

For this reason, Yarn 2 and later are meant to be managed on a by-project basis. Don't worry, little will change! Just make sure to first install the global Yarn binary that we will use to spawn the local ones: 因此，Yarn 2 及更高版本应按项目管理。别担心，改变很小！只需确保首先安装全局 Yarn 二进制文件，我们将用于生成本地二进制：

npm install -g yarn

Once you've followed the instructions (running yarn --version from your home directory should yield something like 1.22.0), go to the next section to see how to actually enable Yarn 2 on your project. 当你你遵循上述说明（从主目录运行应该产生类似），请转到下一节，了解如何在项目中实际启用 Yarn 2。yarn --version1.22.0

You've probably remarked the global Yarn is from the "Classic" line (1.x). This is expected! One extra perk of this system is that projects configured for Yarn 1 will keep using it instead of suddenly having to migrate to the 2.x configuration format. We wouldn't have had to do this if Yarn had been "project locked" from the beginning, but hindsight is 20/20 😉

按项目安装

遵循全局安装的说明
进入你的项目目录：

cd ~/path/to/project

运行以下命令：

yarn policies set-version berry # 针对小于 v1.22 版本
yarn set version berry          # 针对 v1.22+ 版本

"Berry" 是 Yarn 2 发布线的代号，同时也是我们的代码仓库的名称！

提交更改后的 .yarn 和 .yarnrc.yml 文件

更新到最新版本

如果以后要将 Yarn 更新到最新版本，请运行：

yarn set version latest

Yarn 将从我们的网站下载最新的二进制文件，并将其安装在您的项目中。然后，不要忘记更新依赖项并提交更新结果！

安装 master 分支的最新构建版本

随着时间的推移，即使最新版本也不够新了，那么你可能希望尝试最新的 master 代码分支，以检查 Bug 是否已修复。这在 Yarn 2 中已经变得非常简单了！只需运行以下命令即可：

yarn set version from sources

同样的，还可以使用 --branch 参数来指定要安装特定的 PR：

yarn set version from sources --branch 1211