Support for xlink:href

Hey guys,

SVG support is currently incomplete, use does not work because xlink:href is a namespaced attribute that needs the couple setAttributeNS/removeAttributeNS.

I’m not opening a PR directly for this, but it’s a rather common use case and I think we should support it.

Some references:

• preact issue on the subject: https://github.com/developit/preact-svg/issues/15
• preact-way: https://github.com/developit/preact/blob/33fc697ac11762a1cb6e71e9847670d047af7ce5/src/dom/index.js#L81

[leeoniya]

i’m 👍 on this from a practical standpoint. my current concern with adding it to domvm is the perf overhead of testing each attr name for namespace presence in a hot function. since it cannot be cheaply prefix-tested, running a regex of indexOf on every attr would greatly impact perf. there are some options tho.

• in domvm svg elems use their own factory, so perhaps plain vnodes can be saved from the overhead.
• a non-standard extra prefix would be cheap to test more generally: :xlink:href but is surprising
• rather than supporting any namespaced, just explicitly test for xlink:href, which is cheap.

for what it’s worth, i plan to add support for this in domvm, but have to figure out which mix of the above ideas would result in least perf degredation. i think custom prefixing is DOA due to non-uniformity 😦

[ngryman]

@leeoniya @lukejacksonn Thanks for the feedback, let’s continue on this thread where we are discussing an alternative solution for things like this: #211.