Documentation for stateless functions/components, condensed two pages about refs into one

[jimfb]

Condensed the two refs pages into a single refs page, added a note about stateless components having null references.

[jimfb]

@zpao @spicyj Fixes #4913

[jimfb]

Added documentation for stateless components, as per conversation with @spicyj.

[sophiebits]

Can we call it "Refs to Components" here (and in the sidebar, if that's specified somewhere else)?

[jimfb]

@spicyj Fixed, ready to go?

[vramana]

Shouldn't this be ref={(ref) => this.myTextInput = ref} ??

[zpao]

Yes

[zpao]

Actually this should just be ref="myTextInput" since we're talking about string refs.

[zpao]

Normally this isn't an issue, since stateless functions do not provide an imperative API, there really isn't much you could do with an instance anyway.

This doesn't parse as a sentence to me. Maybe split into 2 sentences at the first comma?

[zpao]

Super nit (that I shouldn't actually care much about but that tiny bit of OCD in my brain decided to notice): the rest of our docs uses a single space after periods in a sentence. You used 2 (and not entirely consistently at that). I'm sure you'll ignore this and that's fine.

[jimfb]

Haha, one space for proportional fonts and two spaces for monospace fonts leaves it ambiguous what to do when you're writing .md which will turn into HTML. I went ahead and changed this file to single-space, though we aren't exactly consistent throughout the rest of our docs :).

[jimfb]

Good to go?

[zpao]

nit: leading whitespace is still here (and in the next paragraph, and the one after that… and the one after that but you didn't add that)

[jimfb]

Done.

[zpao]

👍