Yarn is Facebook’s new lightning fast package manager for JavaScript

Facebook today announced a new package manager named Yarn that aims to be a fast, reliable, and secure alternative npm client.

Yarn is a new package manager that replaces the existing workflow for the npm client or other package managers while remaining compatible with the npm registry. It has the same feature set as existing workflows while operating faster, more securely, and more reliably.

The primary function of any package manager is to install some package — a piece of code that serves a particular purpose — from a global registry into an engineer’s local environment. Each package may or may not depend on other packages. A typical project could have tens, hundreds, or even thousands of packages within its tree of dependencies.

These dependencies are versioned and installed based on semantic versioning (semver). Semver defines a versioning scheme that reflects the types of changes in each new version, whether a change breaks an API, adds a new feature, or fixes a bug. However, semver relies on package developers not making mistakes — breaking changes or new bugs may find their way into installed dependencies if the dependencies are not locked down.

Yarn comes with the following features:

• Offline Mode: If you’ve installed a package before, you can install it again without any internet connection.
• Deterministic: The same dependencies will be installed the same exact way across every machine regardless of install order.
• Network Performance: Yarn efficiently queues up requests and avoids request waterfalls in order to maximize network utilization.
• Multiple Registries: Install any package from either npm or Bower and keep your package workflow the same.
• Network Resilience: A single request failing won’t cause an install to fail. Requests are retried upon failure.
• Flat Mode: Resolve mismatching versions of dependencies to a single version to avoid creating duplicates.

Early reports are that is extremely fast and it works similar to Composer in that it creates a lock file and uses that when calling yarn install. Also, Laravel is rumored to already be working on adding the lock file to take advantage of this new package manager and will come installed by default on all new Forge servers.