Important: This documentation covers Yarn 1 (Classic).
For Yarn 2+ docs and migration guide, see

Installing dependencies

If you have just checked out a package from version control, you will need to install those dependencies.

If you are adding dependencies for your project, then those dependencies are automatically installed during that process.

Installing Dependencies

yarn install is used to install all dependencies for a project. The dependencies are retrieved from your project’s package.json file, and stored in the yarn.lock file.

When developing a package, installing dependencies is most commonly done after:

  1. You have just checked out code for a project that needs these dependencies to function.
  2. Another developer on the project has added a new dependency that you need to pick up.

Installing Options

There are many options for installing dependencies, including:

  1. Installing all dependencies: yarn or yarn install
  2. Installing one and only one version of a package: yarn install --flat
  3. Forcing a re-download of all packages: yarn install --force
  4. Installing only production dependencies: yarn install --production

See the full list of flags you can pass to yarn install.