Yarn

Yarn (Berry) is a modern package manager. It introduced Plug’n’Play (PnP) to eliminate node_modules and support Zero Installs.

When to Use

• Monorepos: Yarn Workspaces are robust and feature-rich (Constraints, plugins).
• Speed: PnP is faster than node_modules linking.
• Correctness: Strict phantom dependency checks prevent requiring packages you didn’t list.

Quick Start

corepack enable
yarn set version stable
yarn init -2

# Install
yarn add react

Core Concepts

Plug’n’Play (PnP)

Instead of copying files to node_modules, Yarn generates a .pnp.cjs map. Node requires are intercepted and resolved directly from the cache.

Zero Installs

Commit the .yarn/cache folder. Cloning the repo = Installation complete. No yarn install needed in CI.

Constraints

Enforce rules across workspaces (e.g., “All packages must use React 18”).

Best Practices (2025)

Do:

• Use Corepack: Manage Yarn versions via Node’s corepack tool.
• Use yarn dlx: Equivalent to npx.
• Commit Cache: If using Zero Installs, do commit the binary cache.

Don’t:

• Don’t use Yarn 1: Legacy Yarn (v1) is dead. Migrate to Berry (v4+).

References

• Yarn Documentation