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Yarn Package Manager

The 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.

Package managers are incredibly popular tools, especially in the frontend JavaScript communities. They make it easier for developers to install, update, configure and uninstall code modules within their applications. They do so by communicating with a registry of code modules and manage the various dependencies code modules usually have.

Yarn aims to address issues Facebook have experienced with NPM, particularly in areas such as performance, security, and consistency. This new package manager still has access to the NPM and Bower registries

Ultra Fast

Yarn caches every package it downloads so it never needs to download it again. It also parallelizes operations to maximize resource utilization so install times are faster than ever.

Mega Secure

Yarn uses checksums to verify the integrity of every installed package before its code is executed.

Super Reliable

Using a detailed, but concise, lockfile format, and a deterministic algorithm for installs, Yarn is able to guarantee that an install that worked on one system will work exactly the same way on any other system.


In the Node ecosystem, dependencies get placed within a node_modules directory in your project. However, this file structure can differ from the actual dependency tree as duplicate dependencies are merged together. The npm client installs dependencies into the node_modules directory non-deterministically. This means that based on the order dependencies are installed, the structure of a node_modules directory could be different from one person to another. These differences can cause “works on my machine” bugs that take a long time to hunt down.

Yarn resolves these issues around versioning and non-determinism by using lock files and an install algorithm that is deterministic and reliable. These lock files lock the installed dependencies to a specific version and ensure that every install results in the exact same file structure in node_modules across all machines. The written lockfile uses a concise format with ordered keys to ensure that changes are minimal and review is simple.

The install process is broken down into three steps:

  1. Resolution: Yarn starts resolving dependencies by making requests to the registry and recursively looking up each dependency.
  2. Fetching: Next, Yarn looks in a global cache directory to see if the package needed has already been downloaded. If it hasn’t, Yarn fetches the tarball for the package and places it in the global cache so it can work offline and won’t need to download dependencies more than once. Dependencies can also be placed in source control as tarballs for full offline installs.
  3. Linking: Finally, Yarn links everything together by copying all the files needed from the global cache into the local node_modules directory.

By breaking these steps down cleanly and having deterministic results, Yarn is able to parallelize operations, which maximizes resource utilization and makes the install process faster. Yarn reduced the install process by an order of magnitude, from several minutes to just seconds. Yarn also uses a mutex to ensure that multiple running CLI instances don’t collide and pollute each other, so Hire best yarn developers for fast, reliable and secure dependency management.


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