Yarn Package Manager

Yarn is a package manager for Node-dot-js created by Sebastien Lorber and the Yarn team at Facebook in 2016, providing fast, reliable, and secure dependency management with features including parallel package downloads for faster installation, deterministic lockfiles for reproducible builds, offline caching for installation without network access, workspace support for monorepos, plug-and-play for zero-install workflows, plugin architecture for extensibility, and checksum verification for package integrity, designed as an improvement over npm with a focus on speed, security, and developer experience, adopted by millions of projects and recommended by frameworks including React, Gatsby, and Ember for their development workflows. The deterministic resolution algorithm reads the yarn lockfile to resolve exact package versions, ensuring that every developer and CI environment installs identical dependency trees, with the lockfile containing the exact version, resolved URL, and integrity hash for every package, preventing supply chain attacks through checksum verification, and the resolution supporting both semantic versioning ranges and exact version pinning. The PnP system eliminates the node_modules directory entirely by generating a single JavaScript file that maps package names to their locations in the cache, enabling instant project setup without node_modules installation, zero-install workflows through cache versioning in version control, and reduced disk usage, while the PnP API provides hooks for tools that expect node_modules, ensuring compatibility with existing development tools. The workspace support for monorepos with a single lockfile. The offline cache. The plugin architecture for custom resolvers and fetchers. The constraints for workspace validation. The version policies for automated version bumps. Designed by Sebastien Lorber and Facebook. Designed for Node developers.