Yarn

yarn.lock

• The purpose of a lock file is to lock down the versions of the dependencies specified in a package.json file
  • This means that in a yarn.lock file, there is an identifier (ie. exact version specified) for every dependency and sub-dependency that is used for a project
    • sub-dependencies are the dependencies of a dependency
• The equivalent of yarn.lock for npm is package-lock.json. If using both npm and yarn, we need both of them, and they need to remain in sync (use yarn's import directive to accomplish this)
• if we didn't have a yarn.lock, then if a co-worker cloned our repo and ran yarn install, they may get different versions of a dependency, since package.json can specify version ranges.
  • Instead, since yarn.lock is checked into version control, when the co-worker clones the repo and runs yarn install, yarn.lock will be checked and the version specified will be installed.
• critical to have if working on a team or if working alone with a CI server.
• yarn.lock gets updated any time a dependency is added, removed or modified
  • If we want to ensure yarn.lock is not updated, use --frozen-lockfile
    • The difference between --frozen-lockfile and --pure-lockfile is that the former will fail if an update is needed
• In a perfect world, yarn.lock is unnecessary, because the point of semver is that unless the major version changes, the upgraded package will still work. In other words, if the version in package.json is listed as ^16.0.1, then yarn install is free to go to the latest minor version, which doesn't matter since semver defines that as fully backwards compatible.
  • however, in the real world not everyone follows semver best practices, and sometimes it is just mistakes which ruin backward compatibility

Upgrading packages

• if we have a dependency version in package.json specified at ^3.9.1, this means that any version between 3.9.1 and 4.0.0 will be acceptable. Of course, since we have a lockfile, upgrades will not automatically happen.
• yarn upgrade allows us to upgrade all dependencies in package.json. If we use the ^ specifier, then the latest version within the range will be added. This will be reflected in yarn.lock
• we can ignore the version range by passing the --latest flag.
  • This modifies both yarn.lock and package.json
• We can see all packages that can be upgraded with yarn upgrade-interactive --latest

Link

• yarn link allows us to create symlinks to local projects, from within the project (with package.json) we are currently in.
• ex. if we have a rn-client project and a components project, and we want to use components within rn-client, we can do the following:
  1. go to components project and run yarn link
  2. go to rn-client project and run yarn link components (name field of package.json)
     • this creates a symlink at rn-client/node_modules/components
  3. from rn-client project, import components from 'components'
• It is meant for development-only purposes
• spec: think of yarn link as exporting the package, and yarn link <package> as importing it.

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Children

1. Cook
2. Yarn Workspaces