Should I commit the yarn.lock file and what is it for?

Question

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?

Answer 1

Yes, you should check it in, see Migrating from npm

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.

Answer 2

Depends on what your project is:

1. Is your project an application? Then: Yes
2. Is your project a library? If so: No

A more elaborate description of this can be found in this GitHub issue where one of the creators of Yarn eg. says:

The package.json describes the intended versions desired by the original author, while yarn.lock describes the last-known-good configuration for a given application.

Only the yarn.lock-file of the top level project will be used. So unless ones project will be used standalone and not be installed into another project, then there's no use in committing any yarn.lock-file – instead it will always be up to the package.json-file to convey what versions of dependencies the project expects then.

Answer 3

I see these are two separate questions in one. Let me answer both.

Should you commit the file into repo?

Yes. As mentioned in ckuijjer's answer it is recommended in Migration Guide to include this file into repo. Read on to understand why you need to do it.

What is yarn.lock?

It is a file that stores the exact dependency versions for your project together with checksums for each package. This is yarn's way to provide consistency for your dependencies.

To understand why this file is needed you first need to understand what was the problem behind original NPM's package.json. When you install the package, NPM will store the range of allowed revisions of a dependency instead of a specific revision (semver). NPM will try to fetch update the dependency latest version of dependency within the specified range (i.e. non-breaking patch updates). There are two problems with this approach.

1. Dependency authors might release patch version updates while in fact introducing a breaking change that will affect your project.

2. Two developers running npm install at different times may get the different set of dependencies. Which may cause a bug to be not reproducible on two exactly same environments. This will might cause build stability issues for CI servers for example.

Yarn on the other hand takes the route of maximum predictability. It creates yarn.lock file to save the exact dependency versions. Having that file in place yarn will use versions stored in yarn.lock instead of resolving versions from package.json. This strategy guarantees that none of the issues described above happen.

yarn.lock is similar to npm-shrinkwrap.json that can be created by npm shrinkwrap command. Check this answer explaining the differences between these two files.

Answer 4

I'd guess yes, since Yarn versions its own yarn.lock file: https://github.com/yarnpkg/yarn

It's used for deterministic package dependency resolution.

Answer 5

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.

Answer 6

Yes, You should commit it. For more about yarn.lock file, refer the official docs here

Answer 7

Yes! yarn.lock must be checked in so any developer who installs the dependencies get the exact same output! With npm [that was available in Oct 2016], for instance, you can have a patch version (say 1.2.0) installed locally while a new developer running a fresh install might get a different version (1.2.1).