Add Node DNS as a Webpack mock - PR Linked

Created by: Downchuck

Presently CRA works quite well for isomorphic web applications: I've only hit one strong issue -- node built-ins as required by submodules. So when I hit: "Module not found: Can't resolve 'dns'" with my yarn start, I was unable to work around it, short of manually editing a node module (a pain).

Several libraries have worked to remove dns from their require statements. This issue bubbled from node-postgres, which has a direct require('dns') statement that I've had to comment out. With that done, life just works, for a rather large and complicated, multiple component application.

Unfortunately, I've not found another route.

I attempted to add a stub for dns in package.json, but as "pg" is included from the sub-project, I was unable to work-around the issue. As I'm using serve and build, not test, I don't have Jest mocks to fall back on.

I am doing all I can not to run an eject, as I'd like to stay simple and with the mainline of CRA.

So with all of that said, I'm looking/asking if there is a method for accommodating the peculiar use case of dependencies that have calls to node built-ins, such that they do not break the build.

Obviously I am not asking that we actually make them work -- once the build runs I have no issue mocking those libraries to take different routes.