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yarn (but it would be the same if you used npm as a client) is warning you about unmet peer dependencies. Peer dependencies are different from your usual dependencies in that installing a module will not install its peer dependencies, with the implicit assumption that you already have them, or will need them anyway to use that package.

For example, babel-loader clearly needs Webpack to be used, and instead of bringing it in as a transitive dependency, it expects you to have it in your package.json.

There are a couple of situations where this does not work as expected:

• a package expects a peer dependency with a version, but you have a version number that is incompatible (it might still work though)
• a package might list a peer dependency which you really don't need - for example eslint-config-react-app requires a peer of eslint-plugin-flowtype, which is pointless if you are not using Flow.

How to fix this? by adding those dependencies to your project.