Esprima is a JS parser written in JS that's got pretty good performance, but we're not doing as well as we could. I'll attach a little benchmark. Dave

You can run in-browser benchmarks at the URL. Dave

Nightly - Total 359.6 ms 993.3 ms (slow script dialog) 0.0 ms 154.0 ms Chrome 30 - Total 142.8 ms 221.2 ms 0.0 ms 49.1 ms IE 10 - Total 217.4 ms 241.4 ms 0.0 ms 76.7 ms

We are still a lot slower here. Especially with Traceur. Nightly 127.7 ms 367.9 ms 451.1 ms 112.0 m Chrome 42 39.2 ms 232.5 ms 76.4 ms 50.8 ms

I'll profile this later. I bet there are some interesting perf cliffs.

A shell version of the benchmark. The numbers are better than in the browser and UglifyJS2 seems to be faster than V8 in the shell, but I can reproduce Traceur being about 6x slower, so this will be useful.

For Traceur, we have the usual suspects: (1) About 25% under CreateThis* stubs. This is bug 1129387 and seems to affect a ton of different benchmarks lately. I want to fix this very soon. (2) Some highly polymorphic GETPROPs. This is bug 965793, though there are alternatives to that approach, like Luke's reverse-shape idea. This is a pretty typical performance issue for scripts that build a tree and access properties of parent nodes, unfortunately. (3) Some arguments object stuff, filed bug 1131996 and bug 1132004.

Biggest problem with Esprima is that we spend 15-20% of the time under Nursery::collect, almost half of that is under Nursery::moveToTenured. Maybe our pretenuring heuristics don't work, or we're simply creating a ton of garbage. Acorn spends about 10% under Nursery::collect. It also has some slow stuff like NewDenseArray and InitElementArray, I have to investigate this more. (In reply to Jan de Mooij [:jandem] from comment #9) > (1) About 25% under CreateThis* stubs. This is bug 1129387 and seems to > affect a ton of different benchmarks lately. Add Esprima and UglifyJS2 to the list.

Apparently the site changed... the tests are longer and there are new ones. Nightly 42 / Chrome 43 Esprima 2.4.1: 344.8 ms / 306.6 ms UglifyJS2: 642.3 ms / 1097.9 ms Traceur: 735.2 ms / 397.2 ms Acorn 1.0.1: 523.1 ms / 323.9 ms Shift: 1732.1 ms / 1633.6 ms Shift (no early errors): 279.1 ms / 203.0 ms Results are much better than before.