[nachtigall]

What's the difference between IonMonkey and Firefox' SpiderMonkey?

[azakai]

IonMonkey is the name of one of the JITs in SpiderMonkey.

(For entertainment purposes, the JITs have names ending in -Monkey.)

[dsp1234]

IonMonkey is to SpiderMonkey as TurboFan[0] is to V8

[0] - https://github.com/v8/v8/wiki/TurboFan

[kannanvijayan]

I'd compare IonMonkey in SM to Crankshaft in V8. Ion was actually started in response to Crankshaft.

TurboFan is a new even-higher-tier, even-more-expensive-to-compile, but potentialy even-more-optimized compiler backend the V8 team is working on.

[twotwotwo]

Spelled out, TurboFan and IonMonkey are JITs that take longer to run but can do more optimizations. The idea is to run them on code that executes a _lot_ of times, so the faster code generated pays for the extra JIT time. If you wrote a game in straight JS and it contains some code that runs for a bunch of in-game objects every frame, that's the kind of thing these JITs could really help with.