# Yarn — Modern JavaScript Package Manager with Plug'n'Play

> Yarn is a fast, reliable JavaScript package manager with workspaces, offline caching, and an optional Plug'n'Play install strategy that eliminates node_modules.

## Install

Save in your project root:

# Yarn — Modern JavaScript Package Manager with Plug'n'Play

## Quick Use
```bash
corepack enable
yarn init -2
yarn add react
yarn install
```

## Introduction
Yarn is a JavaScript and TypeScript package manager created to solve consistency and performance problems in the npm ecosystem. Its modern version (Berry / Yarn 4) introduces Plug'n'Play, workspaces, and strict dependency resolution by default.

## What Yarn Does
- Installs npm-compatible packages with deterministic lockfile resolution
- Supports workspaces for monorepo dependency management
- Offers Plug'n'Play (PnP) mode that removes the need for `node_modules`
- Provides offline mirroring so installs work without network access
- Enforces strict peer dependency rules to catch version conflicts early

## Architecture Overview
Yarn 4 (Berry) is written in TypeScript and ships as a single self-contained JS file committed to your repo via `.yarn/releases`. It resolves dependencies from the lockfile (`yarn.lock`), fetches compressed archives into a global or local cache, and in PnP mode generates a `.pnp.cjs` loader that maps import requests to zip entries without extracting to disk.

## Self-Hosting & Configuration
- Enable Corepack (`corepack enable`) so the correct Yarn version is used per project
- Set the Yarn version per repo with `yarn set version stable`
- Configure `.yarnrc.yml` for registry URLs, PnP settings, and plugin paths
- Use `yarn workspaces foreach` to run scripts across monorepo packages
- Store the cache in `.yarn/cache` and commit it for fully offline CI

## Key Features
- Plug'n'Play eliminates `node_modules` for faster installs and stricter resolution
- Built-in workspace support for multi-package repositories
- Constraints engine lets you enforce dependency rules across a monorepo
- Extensible via plugins (TypeScript, interactive tools, workspace utilities)
- Corepack integration ensures contributors use the exact same version

## Comparison with Similar Tools
- **npm** — ships with Node.js and works everywhere; Yarn adds PnP, workspaces constraints, and offline installs
- **pnpm** — uses a content-addressable store and hard links; Yarn PnP avoids disk extraction entirely
- **Bun** — all-in-one runtime with a built-in package manager; Yarn focuses purely on dependency management
- **Turbo** — monorepo task runner; Yarn manages dependencies while Turbo orchestrates builds on top

## FAQ
**Q: Is Yarn 4 backwards-compatible with Yarn 1 (Classic)?**
A: The CLI commands are mostly compatible, but the internals differ significantly. Yarn 1 is in maintenance mode; migration to Yarn 4 requires running `yarn set version berry`.

**Q: Do all Node libraries work with Plug'n'Play?**
A: Most do. Packages that rely on undeclared dependencies need a `packageExtensions` entry in `.yarnrc.yml`. The ecosystem compatibility is high.

**Q: Can I still use node_modules instead of PnP?**
A: Yes. Set `nodeLinker: node-modules` in `.yarnrc.yml` to fall back to the traditional layout.

**Q: How does Yarn handle security auditing?**
A: Run `yarn npm audit` to check for known vulnerabilities in your dependency tree, similar to `npm audit`.

## Sources
- https://github.com/yarnpkg/berry
- https://yarnpkg.com/

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Source: https://tokrepo.com/en/workflows/b49e4acf-40e3-11f1-9bc6-00163e2b0d79
Author: AI Open Source