Yarn Berry

rm -rf ./**/node_modules

What is Yarn?

Yarn is an alternative package manager to npm. It's been around since 2016.

Yarn's claim to fame is stability. It aims to have a deterministic installation; given a yarn.lock file, Yarn will always create the some node_modules tree.

We use Yarn in the monorepo!

What is Yarn Berry?

Yarn Berry is the codename for a complete rewrite of the Yarn codebase that started two years ago.

All new versions of Yarn (the latest is 3.1.0) live in the yarnpkg/berry GitHub repo.

In addition to PnP-by-default, the new Yarn architecture is composed of small modules with intentional API surfaces. It also includes a plugin framework that can make use of these new modules.

Oh, also

You check it in to your repo!

Why should I migrate off of Yarn v1?

New plugin API allows for really awesome new workflows, PnP improves performance and stability, and Zero-Installs improve development experience and CI performance.

Also... Yarn v1 is deprecated and will not receive any future updates!

What do I get out of it?

A bunch of stuff! But first we need to explain some things we've been glossing over.

Plug'n'Play

It should be the package manager's job to inform the interpreter about the location of the packages on the disk and manage any dependencies between packages

Yarn already knows everything there is to know about your dependency tree - it even installs it on the disk for you. So, why is it up to Node to find where your packages are?

Installs are now nearly instantaneous. Yarn only needs to generate a single text file (instead of potentially tens of thousands). The main bottleneck becomes the number of dependencies in a project rather than disk performance.
Installs are more stable and reliable due to reduced I/O operations. Especially on Windows (where writing and removing files in batches may trigger various unintended interactions with Windows Defender and similar tools), I/O heavy node_modules operations were more prone to failure.
Perfect optimization of the dependency tree (aka perfect hoisting) and predictable package instantiations.
The generated .pnp.cjs file can be committed to your repository as part of the Zero-Installs effort, removing the need to run yarn install in the first place.
Faster application startup! The Node resolution doesn't have to iterate over the filesystem hierarchy nearly as much as before (and soon won't have to do it at all!).

Zero-Installs

Make your projects as stable and fast as possible by removing the main source of entropy from the equation: Yarn itself.

What does that actually get us, practically?

Dramatically reduced install time in CI. git clone takes an extra 15 or 20 seconds, and that's... it. Nothing else needs to be downloaded or written to disk. This led to a 4-minute+ decrease in build time for Oak.
Switching branches? That's all you need to do. No need to run yarn install, yarn clean, rm -rf ./**/node_modules, what have you.
Yarn will now tell you if your packages attempt to import modules they don't declare a dependency on.
Real plugins! Have a thing you wished Yarn did for you? Now you can add support for that thing!

Ok, ok. But how?

.npmrc → .yarnrc.yml
Janky freeze-workspace script → yarn-plugin-isolate-workspace
New workspace: protocol
Install and set up Git LFS for .cache/*.zip
Install the Yarn SDKs for your editor
Run yarn install and fix missing dependencies in your packageExtensions configuration. Repeat this ad nauseam until Yarn stops complaining.