discussion: add cssGlobal

[mattkrick]

Aphrodite is a lightweight package for modular styles. That's why we love it.
But some things aren't modular:

• fonts
• global resets/normalizers
• 3rd party css overrides

The current best practice is to use something other than aphrodite for these cases (except in the case of fonts, where aphrodite has kinda hacky logic).

With a very small amount of code, we can support globals (including SSR).

Globals are actually very easy:

• They only need to be called once (no dependency on context/state/props)
• Aphrodite doesn't need to worry about cascade order because globals should be written as specific as necessary
• It allows aphrodite to get rid of that messy font handling (will adjust this PR if you like where this is going)

Why a 3rd party package doesn't work:

• isBuffering is private, which means the user must pass injectStyleOnce to their function (otherwise you'd have 2 discrete flush cycles for the SSR). This is doable: see hepha. However, it'd be so much cleaner to include it in aphrodite as I'm sure everyone has a custom font, or {margin: 0} body tag that they'd like to load properly 😄

[kentcdodds]

Unless I'm mistaken, this requires a polyfill. This project's probably not ready to drop Internet Explorer :)

[mattkrick]

Yeah, Edge+ (http://kangax.github.io/compat-table/es6/#test-WeakSet).
A weakset is used on the off chance that someone creates their globalStyles inside the render loop, as that'd create a memory leak.
If people use it like they should a Set works just fine.

[jlfwong]

Hi @mattkrick,

Thanks for the thoughtful discussion!

Having support for global styles should be possible once #95 lands, and I'd prefer not to provide multiple mechanisms for it.

This PR doesn't work for SSR since it doesn't reset the injectGlobals anywhere. That aside though, I think this use case should be covered by #95, so I'm going to close this.

Let me know if I'm misunderstanding