support for IE

[lwhorton]

Once again, great job on this lib. It's nearly-exactly what I would have written myself, so thanks for saving a ton of time.

It would be great to support later IE versions. Currently IE doesn't support css-vars. You can really easily get around this by outputting both a var and a fallback style.

a {
  color: #7F583F;
  color: var(--primary);
}

I'm not sure what the implementation implications are for this change, so some input would be great.

[roman01la]

I don't really plan to support browsers without CSS Variables support. Are you sure ClojureScript perf is fine on IE <11? Runtime styles may make it even worse.

[lwhorton]

Ah that's a bummer. Would it be a lot of work to support this? Unfortunately it's not <11 i'm worried about; even 11 doesn't support css vars (thanks to Edge, probably).

I'm not positive how you're converting a map into a string of css rules. But, it doesn't seem like a lot of extra work to make sure to also add a rule: actual-value-not-var before each var insertion, which would provide backwards support. If this is something you're open to I would consider providing a patch, since I really like this lib but also have to support IE11.

[lwhorton]

I have to support an IE11 client, unfortunately. I am going to fork this library and poke around for where I can best insert this change without breaking anything. If you had any pointers on where to start and what effects I might want to watch out for, that would be much appreciated :)

[roman01la]

Essentially you have to move macros into runtime. IE11 doesn’t have the best JS VM so I’m not sure if perf is going to be fine there. I’d make a wrapper on top of existing JS libraries instead.