Yarn acts as the package manager for the javascript libraries.
Instead of using gems for the corresponding js libraries yarn can be used.
The advantages are many: (Pointing a couple)
  - we don't have to wait for a gem to be made for a js library
  - we don't have to wait for the gem to be updated when a new version of the library is released.


Yarn adds the packages to the folder `node_modules`.
So the assets path will have to be updated at
`config/initializers/assets.rb`.
The following line will have to be uncommented.
`Rails.application.config.assets.paths << Rails.root.join('node_modules')`.

Yarn creates a `yarn.lock` file to lock the versions.
`yarn init` can be done to populate `package.json` ( Consider this similar to `Gemfile`, and `yarn.lock` to `Gemfile.lock`)