Enable rendering into shadow roots

[BinaryMuse]

This adds the shadow root nodeType to the list of node types that can be rendered into.

I have completed the CLA.

Please let me know if I left anything out!

[martinandert]

Would you mind explaining what this is good for?

[petehunt]

I know you are just following what's already here, but I think we should consolidate these constants

[petehunt]

Does this work correctly with event handling?

[BinaryMuse]

@martinandert I'm specifically using it with x-tags, (see https://github.com/BinaryMuse/x-tag-react-hello-world), but more generally I think it makes sense to allow rendering into any node (that actually works as a mount point).

@petehunt Yes; I've added a click handler to the demo at https://github.com/BinaryMuse/x-tag-react-hello-world and it seems to work fine. I'd be happy to perform some additional testing along these lines.

Additionally, I'd be happy to extract those constants; I'll look at this sometime today.

[plievone]

@BinaryMuse could you check #859 and #840 too, if your pull request addresses those concerns?

[plievone]

If you grep nodeType through React codebase, there are a couple of other places where for example TEXT_NODE is hardcoded as 3, don't know if those should be included too (some of those may be vendored in) or perhaps in another pull request.

[andreypopp]

Why not just use Node.ELEMENT_NODE and the likes? Probably all the places where you want to check for nodeType already access DOM so it should be safe? See https://github.com/facebook/react/pull/423/files#r7112182 for the previous discussion on the matter

[syranide]

@andreypopp Not all browsers we support has Node.ELEMENT_NODE, etc.

[andreypopp]

@syranide right... IE8...

[plievone]

@andreypopp Related: #893

[sebmarkbage]

I'm (irrationally) scared of these enum modules because I'm never sure if they'll get inlined or not. If they're not inlined, then they might not minify well and might also be a perf cost. It's probably irrational but let's just keep it as constants in the individual modules for now. The reason for having it separate is usually because it might change, but these won't. :)

I'm not quite sure what the expected behavior is for the events. Can we add a test that asserts the expected behavior? If it's not possible to test in JSDOM at the moment, it's fine to have a disabled test for now.

[sophiebits]

This looks stale.