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Yarn Package Manager: Detailed Notes

Yarn is a package manager for JavaScript that was developed by Facebook in collaboration with other developers as an alternative to npm (Node Package Manager). It aims to solve issues related to performance, security, and consistency in dependency management. Here is a detailed look at Yarn:

Key Features

  1. Speed:

    • Yarn uses a caching mechanism that significantly speeds up package installations. Once a package is downloaded, it gets cached, and subsequent installations can retrieve it from the local cache, making the process faster.
    • Parallel operations allow Yarn to perform multiple tasks concurrently, reducing the overall installation time.

  2. Deterministic Dependency Resolution:

    • Yarn generates a yarn.lock file that ensures the exact same version of dependencies are installed across all environments. This lockfile guarantees consistency and helps avoid "works on my machine" issues.

  3. Offline Mode:

    • Since Yarn caches every package it downloads, you can install dependencies even when offline, provided they have been installed before.

  4. Security:

    • Yarn uses checksums to verify the integrity of every installed package before its code is executed. This prevents the installation of corrupted or tampered packages.

  5. Network Resilience:

    • Yarn is designed to handle network issues gracefully, retrying requests as needed to ensure successful installations.

  6. Workspaces:

    • Yarn supports monorepos, which allows you to manage multiple packages within a single repository. Workspaces can share dependencies between packages, reducing duplication and improving efficiency.

Installation

To install Yarn, you can use npm or your preferred package manager:

npm install -g yarn

Alternatively, you can follow the installation instructions for different operating systems from the official Yarn website.

Basic Commands

  • Initialize a new project:

    yarn init

  • Add a dependency:

    yarn add <package-name>

  • Add a development dependency:

    yarn add <package-name> --dev

  • Remove a dependency:

    yarn remove <package-name>

  • Install all dependencies:

    yarn install

  • Upgrade a dependency:

    yarn upgrade <package-name>

Advanced Features

Workspaces

Workspaces are a feature that lets you organize your project into separate packages, all within a single repository. This is particularly useful for monorepos.

  • Creating a Workspace:
    1. In your root directory, add a package.json with the following configuration: 
      {
  "private": true,
  "workspaces": [
    "packages/*"
  ]
}
    2. Create subdirectories under packages/ for each workspace package, each with its own package.json.

Scripts

Similar to npm, Yarn allows you to define custom scripts in your package.json.

{
  "scripts": {
    "build": "webpack --config webpack.config.js",
    "test": "jest"
  }
}
  • Running Scripts: 
    yarn run build
yarn run test

Plug'n'Play (PnP)

Plug'n'Play is a new installation strategy that Yarn offers to improve performance and compatibility. Instead of installing node_modules, Yarn writes a single .pnp.js file that maps the entire dependency tree.

  • Enable PnP: 
    yarn set version berry
yarn config set pnpMode loose

Comparing Yarn and npm

  • Speed: Yarn is generally faster due to parallel installation and caching.
  • Security: Yarn has built-in integrity checks to ensure the security of packages.
  • Determinism: Yarn’s lockfile ensures consistent installations.
  • Workspaces: Yarn’s workspace feature simplifies managing monorepos.
  • Community and Compatibility: npm has a larger community and more widespread use, but Yarn is highly compatible with npm registries.

Conclusion

Yarn is a powerful and efficient package manager that addresses many of the shortcomings of npm, particularly in terms of speed, security, and consistency. With features like workspaces and Plug'n'Play, Yarn offers advanced capabilities that can significantly enhance the workflow of developers working with JavaScript and Node.js projects. Whether you are working on a simple project or a complex monorepo, Yarn provides the tools to manage your dependencies effectively.