Intro to Yarn

Yarn is a JavaScript Package Manager, a direct competitor of npm, and it’s one of Facebook most popular Open Source projects.

It’s compatible with npm packages, so it has the great advantage of being a drop-in replacement for npm.

The reason you might want to use Yarn over npm are:

  • faster download of packages, which are installed in parallel
  • support for multiple registries
  • offline installation support

To me offline installation support seems like the killer feature, because once you have installed a package one time from the network, it gets cached and you can recreate a project from scratch without being connected (and without consuming a lot of your data, if you’re on a mobile plan).

Since some projects could require a huge amount of dependencies, every time you run npm install to initialize a project you might download hundreds of megabytes from the network.

With Yarn, this is done just once.

This is not the only feature, many other goodies are provided by Yarn, which we’ll see in this article.

In particular Yarn devotes a lot of care to security, by performing a checksum on every package it installs.

Tools eventually converge to a set of features that keeps them on the same level to stay relevant, so we’ll likely see those features in npm in the future - competition is nice for us users.

Install Yarn

While there is a joke around about installing Yarn with npm (npm install -g yarn), it’s not recommended by the Yarn team.

System-specific installation methods are listed at https://yarnpkg.com/en/docs/install. On MacOS for example you can use Homebrew and run

brew install yarn

but every Operating System has its own package manager of choice that will make the process very smooth.

In the end, you’ll end up with the yarn command available in your shell:

Yarn command installed

Managing packages

Yarn writes its dependencies to a file named package.json, which sits in the root folder of your project, and stores the dependencies files into the node_modules folder, just like npm if you used it in the past.

Initialize a new project

yarn init

starts an interactive prompt that helps you quick start a project:

Running yarn init

Install the dependencies of an existing project

If you already have a package.json file with the list of dependencies but the packages have not been installed yet, run

yarn

or

yarn install

to start the installation process.

Install a package locally

Installing a package into a project is done using

yarn add package-name

This is equivalent to running npm install --save package-name, thus avoiding the invisible dependency issue when running npm install package-name, which does not add the dependency to the package.json file

Install a package globally

yarn global add package-name

Install a package locally as a development dependency

yarn add --dev package-name

Equivalent to the --save-dev flag in npm

Remove a package

yarn remove package-name

Inspecting licenses

When installing many dependencies, which in turn might have lots of dependencies, you install a number of packages, of which you don’t have any idea about the license they use.

Yarn provides a handy tool that prints the license of any dependency you have:

yarn licenses ls

The yarn packages licenses visualized

and it can also generate a disclaimer automatically including all the licenses of the projects you use:

yarn licenses generate-disclaimer

Disclaimer generated by yarn

Inspecting dependencies

Do you ever check the node_modules folder and wonder why a specific package was installed? yarn why tells you:

yarn why package-name

The result of yarn why

Upgrading packages

If you want to upgrade a single package, run

yarn upgrade package-name

To upgrade all your packages, run

yarn upgrade

But this command can sometimes lead to problems, because you’re blindly upgrading all the dependencies without worrying about major version changes.

Yarn has a great tool to selectively update packages in your project, which is a huge help for this scenario:

yarn upgrade-interactive

Upgrading packages with yarn

How to upgrade Yarn

At the time of writing there is no auto-update command.

If you used brew to install it, like suggested above, simply use:

brew upgrade yarn

If instead you installed using npm, use:

npm uninstall yarn -g
npm install yarn -g