I did for my emulator jor1k. Take a look:

https://github.com/s-macke/jor1k/blob/master/js/worker/or1k/...

Handwritten asm.js code. Around 10 hours or porting time.

That's quite an impressive implementation! I didn't realize hand-written asm.js could be that readable.

Yes, more or less. Every operation must be written, that the type is obvious for the compiler. And you have one array, the heap with some special index rules. For example: (r[((ins >> 9) & 0x7C)>>2]|0 The >>2 and |0 is necessary.

People wanting high performance. For example, Grant Galitz's IodineGBA had some portions in asm.js https://github.com/taisel/IodineGBA

No, it doesn't. Where in IodineGBA do you see any hand-written asm.js code?

Here's are some quotes from the author of that very library:

"asm.js requires a style of coding only compilers can output. A person writing actual asm.js code by hand would need to be insane as asm.js code required style of coding is horribly disorganized"[1]

"Unfortunately asm.js requires one giant array to put things on. No one in their right mind codes like that by hand."[2]

1: https://github.com/taisel/IodineGBA/issues/16#issuecomment-2... 2: https://github.com/taisel/IodineGBA/issues/16#issuecomment-2...

That's from 2013. There have been more recent discussions.