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Managing Yarn Dependencies

On Your Machine

FxA uses Yarn to manage its Node dependencies. Follow the Development Setup guide for how to install Yarn and the yarn command on your machine.


Once upon a time FxA used npm to manage its dependencies, which means you may come across documentation or commands that still reference its usage. In most cases you should be able to freely replace the keyword npm with yarn, but it's worth learning about the differences between the two CLIs.

We have a lot of dependencies, and they're constantly updating, so be sure to occasionally run yarn install to stay up-to-date.


If yarn install is failing run yarn -v and check that it is at least 1.22.0. Run npm install -g yarn to update to the latest version if needed.


We have a script that can automatically detect changes to the yarn.lock file and run yarn install when you check out a branch or pull in latest. To enable it set FXA_AUTO_INSTALL=1. If you don't enable it, you'll see a warning when changes are detected letting you know to run yarn install manually.

Dependabot Pull Requests

We use GitHub's Dependabot to automatically update our dependencies.

It runs daily, opening Pull Requests whenever a update is available for any of our many packages' dependencies. PRs will automatically request a review from the @mozilla/fxa-devs GitHub group. FxA engineers are expected to occasionally pitch in with reviewing and merging these PRs.

Click here to see all open Dependabot PRs.

A note about resolutions for sub-dependencies

Resolutions may not work for sub-dependencies. If adding a resolution for a dependency in package.json is not picked up by yarn.lock, you might need to set the resolution manually (this will need to be done for each installed version of the dependency that needs to be resolved).

This generally happens when a dependency has not updated one of it's sub-dependencies, and we would like to force an update for that sub-dependency in our project.

For example, if yarn.lock has package@npm:1.1.1, package@npm:^1.2.0 and the dependency needs to be resolved to 1.3.0, 2 commands will need to be run (with 'package' here replaced with the name of the dependency that needs to be resolved):

yarn set resolution package@npm:1.1.1 '>1.3.0'
yarn set resolution package@npm:^1.2.0 '>1.3.0'