>Duktape is slower than most browsers due to only being interpreted with no JIT.Thinking about it, that shouldn't be an issue, since I believe that most 6502s are only 1-2 MHz.
It takes well over 2 GHz with Higan (nee bsnes) just to emulate a SNES, and that's using a combination of highly tuned C, C++, and assembly (including some crazy hacks like libco which uses some CPU instructions that no compiler can take advantage of).
Wow, this is embarrasing. Even on Windows XP, running ye olde Netscape 7, with the execution cap lowered to make the speed more realistic, it's still significantly fasterhttps://db.tt/jgZZ9lYL
On the other hand, for a system with few chips, you can almost always get away with slower languages. There is a GB, GBC, and GBA emulator written in JS that runs acceptably with pretty good accuracy, even on the pre-JIT Firefox versions. If you are mostly worried about a single chip emulation (which is what the GB is, almost entirely) then you will be just fine. Once you start adding other components of the system it may become an issue.
See my post above. My suspicion is that you need to cool it on the FlipScreen() calls. Like I said though, without seeing your code it's hard to know what's wrong.