Yarn creates a yarn.lock file after you perform a yarn install.
Should this be committed to the repository or ignored? What is it for?
From My experience I would say yes we should commit yarn.lock file. It will ensure that, when other people use your project they will get the same dependencies as your project expected.
From the Doc
When you run either yarn or yarn add , Yarn will generate a yarn.lock file within the root directory of your package. You don’t need to read or understand this file - just check it into source control. When other people start using Yarn instead of npm, the yarn.lock file will ensure that they get precisely the same dependencies as you have.
One argue could be, that we can achieve it by replacing ^ with --. Yes we can, but in general, we have seen that majority of npm packages comes with ^ notation, and we have to change notation manually for ensuring static dependency version.But if you use yarn.lock it will programatically ensure your correct version.
Also as Eric Elliott said here
Don’t .gitignore yarn.lock. It is there to ensure deterministic dependency resolution to avoid “works on my machine” bugs.