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Putting Yarn Package Manager to the test

11/22/2016 β€” 3 min read

What is Yarn?


How does it achieve all of this?

It uses caching to speed up installs by only ever downloading them once and parallelizes operations to maximise resource utilisation.

It uses checksums to verify every package before installing.

It is deterministic so if you check in your lockfile, you can guarantee every developer who yarn installs will get the exact same dependencies as you.

How do I get Yarn?

According to the yarn installation website you can install yarn with the standard OS package managers. I use a mac so I tried to install it with brew (brew update && brew install yarn) but I had issues with this particular installation.

I then discovered you can install yarn via npm, which on some level feels like cheating on npm but anyway... $ npm i -g yarn will install yarn globally. You can check this was successful by $ yarn --version and making sure you get a version number back. This time the installation was fine and I was ready to get down to testing.

Is this really as good as they say?

I wanted to test against a well known project so I cloned the React git repository.

Before each test I ran $ rm -rf node_modules to remove my node modules and start with a clean slate each time. And just to be fair and make sure I really start the yarn installs with a cold cache, I ran $ yarn cache clean before starting the yarn tests.

#Test one - NPM

$ time npm install

First time round:

npm i 48.39s user 15.08s system 106% cpu 59.727 total

Second time round:

npm install 44.50s user 13.40s system 106% cpu 54.331 total

#Test Two - Yarn

yarn install

First time round - cold cache

✨ Done in 29.48s.

Second time round - warm cache

✨ Done in 14.05s.


With a warm cache, yarn installs are around 3 times faster than npm on average from my tests. That's an incredible savings when you have a project with a huge dependency list.

I've started using Yarn on the project I work on. It's brought the local install time down from ~123s to ~40s with a warm cache.

I've not put it into production just yet but I think there are a lot of gains to be made using Yarn as your package manager.

A cool feature of yarn is yarn upgrade-interactive, just merged in last week. It allows you to interactively upgrade packages in a nice command line tool.

*Bonus coolness: They have managed to get /u/Shitty_Watercolour from Reddit to do all the illustrations for the yarnpkg website*

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