Use sets instead of arrays

[tbranyen]

This greatly improves the object pooling performance. No longer do we need to worry about checking indexOf on giant arrays.

[tbranyen]

Ping @jmeas no more array.length - 1 :D

[jamesplease]

Still reviewing the code...one thought is that you'll want to update the documentation somewhere to let people know that they'll need to include the Babel polyfill for Sets to work in all env's, unless diffHTML is limited to only the latest-and-greatest browsers?

[tbranyen]

True, but we also use WeakMap which isn't everywhere either. Since we're aren't going to be able to easily polyfill into Web Worker environments, it might make sense to just limit our scope to evergreen browsers.

[jamesplease]

A succinct way to rewrite this would be:

var reAlloc = [...cache.allocated];

This compiles to [].concat() though, which creates a dynamically sized array. I wonder how that compares speed-wise to the push system you've got going. In any event, I'd expect that fixing the size would be faster than both, but I'd be curious to see the perf diff.

var reAlloc = new Array(cache.allocated.length);
cache.allocated.forEach((v, i) => reAlloc[i] = v);

Wait nvm cache.allocated is now a Set, so the first alternative wouldn't work. The second one (with the fixed-length array) should, tho' if ya swap length for size in the snippet

[tbranyen]

I tried using this before, but babel compiles down to Array.from which is not available in PhantomJS. I polyfilled it there, but then it was not available in Web Workers, which seems like a huge pain to try and polyfill.

[jamesplease]

Ah, okay. Well dang. ha.