>By contrast, LuaJIT can absolutely wreck V8 performance-wise
Not really. Basically on par.
Not really. Basically on par.
Maybe my information is out of date, but I just now picked a random benchmark (the fasta one from the language shootout) and ran it against v8-3.14.5.10 and luajit-2.0.3 (Fedora 21, latest available via yum), and luajit came out quite a bit ahead. I grant that it's a really naive benchmark setup and shouldn't be taken seriously, but my investment here is pretty minimal :)
$ time luajit-2.0.3 fasta.lua 25000000 > /dev/null
luajit-2.0.3 fasta.lua 25000000 > /dev/null 8.60s user 0.01s system 100% cpu 8.613 total
$ time d8 --nodebugger fasta.js > /dev/null -- 25000000
d8 --nodebugger fasta.js -- 25000000 > /dev/null 12.80s user 0.51s system 100% cpu 13.209 total
Those are in the same order of magnitude even! Not even 2x the speed. Hardly makes a difference in picking one or the other, all other things being the same.
Now, compare V8 or LuaJit with Python or Ruby -- that would be "wrecking it".
I'm not attacking v8 here. I'm simply pointing out that there are VMs for interpreted languages which run faster than v8, which isn't to say "v8 is bad", but rather "different languages inherently have different performance profiles".
Though I must admit V8 could handle dictionaries a bit better - but at the moment it does not.