improvements: set react and react-dom alias in webpack

Created by: maomaoZH

set react and react-dom alias in webpack to avoid loading twice react during developing. This issue has been discussed, see here https://github.com/facebookincubator/create-react-app/issues/675. I have tested with my app locally. The duplicated react issue is gone after set up alias.

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Created by: gaearon

I feel like in a way this just works around the problem instead of solving it. I would prefer it we completely failed the build with multiple react / react-doms and printed where they are in the tree so you could figure out how to deduplicate them and fix the root issue.

Created by: maciej-ka

I wonder how it's possible to deduplicate. npm link perhaps?

Created by: gaearon

It depends on the exact scenario in which you're seeing duplication (there are many possible solutions).

Created by: maomaoZH

Okay, let me explain the case that we've been facing. Then we may understand/talk the way how we resolve it. After that, I can improve this pull request.

First, we have an application which is obviously created by create-react-app and using a dependency that we have been developing. That dependency contains our React UI components. Therefore, we need to link the dependency to our main application during the development. So this case cause multiple copies of React issue.

I think that we may resolve the issue in this way that we have in this branch. Besides that, there is such a workaround, here. But the latter one would be a real workaround than the changes we have here in my opinion.

Therefore, I'm wondering how we can resolve the issue. Could you explain that?

Created by: gaearon

We are tracking the "npm link" use case in https://github.com/facebookincubator/create-react-app/issues/1107. Not sure if there's any great solutions for it.

Ideally I'd like us to fix https://github.com/facebookincubator/create-react-app/issues/1333. This wouldn't solve "linking" per se, but it would add a supported way to develop components alongside the app. Would that satisfy your use case?

The reason I'm not very happy with aliasing react and react-dom in particular is because the problem with links still exists: we just work around it for two particular packages. You may still bump into it with other dependencies. So I'd like to see if we can solve this more holistically.

Created by: gaearon

Related: https://github.com/facebookincubator/create-react-app/issues/3883

Seems like this is actually the root of the problem. Pardon the module resolution pun.

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