Hi Vanessa,

Sorry for the delay in responding - as somebody who has been inspired by your SqueakJS project, I think I should mention that I am working on a related project, for now tentatively called JsSqueak.

In addition to the inspiration provided by SqueakJS, it also scratches my longstanding itch about compiling (transpiling) Squeak.

I hesitated to talk about it, as it is still a work in progress - after small bits and pieces that I worked on over a long period, I had the opportunity to spend a significant and uninterrupted chunk of time on it last summer, when I was unemployed for 3 months, and I was able to make good progress. I was optimistically thinking of releasing a first version before the end of last year, but after I started working on my new job, progress on JsSqueak has slowed down significantly. I must confess that I (and especially my wife) hesitate in recreating that productive unemployed situation :)

I started with Squeak 4.5 - I already had code transforming Smalltalk code to a form more suitable for translation - and I also started with VMMakerJS-dtl.18 for the plugin generation part. Of course, I had to heavily modify it, since I have to get rid of the stack usage for arguments/receiver and returns.

Both of these big parts are working. I also implemented most numbered primitives by hand - they are inlined at generation time in the methods calling them.

I am also taking advantage of the latest and greatest additions to JavaScript. I am, of course, using classes, and the parallel class-side hierarchy is implemented using statics. To implement green threads/process switching, all translated methods are implemented as generator functions, and all calls are through yield* expressions. The preemption/interrupt check points are inlined. With this, a process switch is achieved by simply yield-ing (in the process/semaphore primitives).

With this, the Integer>>#benchFib method is translated (as a method in Number.prototype, there is one more, simpler, implementation in BigInt) as:

*_benchFib() {
   if (Number.isSafeInteger(this.valueOf())) { // Effective (inherited or local) source for #benchFib in SmallInteger
      /*Handy send-heavy benchmark*/
   /*(result // seconds to run) = approx calls per second*/
   /* | r t |
     t := Time millisecondsToRun: [r := 26 benchFib].
     (r // 1000) // t*/
   /*138000 on a Mac 8100//100*/
   if (GlobalActivationCounter-- < 0) yield* GlobalCheckForInterrupts();

   return (yield* this._lt( 2)).booleanValueOf("questionMark:colon:") ? (1) : (yield* (yield* (yield* (yield* this._sub( 1))._benchFib())._add( yield* (yield* this._sub( 2))._benchFib()))._add( 1));
} else // No implementation for #benchFib in Float hierarchy, trigger a DNU
      return yield* super._benchFib()
}

The top-level check for smallIntegers is because both SmallInteger and Float are mapped to Number.

The booleanValueOf call is for implementing the mustBeBoolean machinery (it actually translates directly to DNU, like it is done nowadays in Squeak).

Of course, in Boolean, booleanValueOf is just an alias for valueOf

As you can see, though, this is not terribly efficient, but there is room for improvement/optimizations. With more work, in this case, the _lt call could be replaced by the < operator, and even the _sub and _add calls could be optimized, 
although not completely, since their result can morph into LargeInteger (mapped to BigInt).

As hinted above, SmallInteger is mapped to Number (in the safeInteger range), Float is mapped to Number as well, and LargeInteger is mapped to BigInt.

BlockClosure is mapped to Function, Boolean is mapped to Boolean, Character is mapped to String, weak references are implemented via WeakRef. 
I have briefly considered also doing slightly higher-level mappings, for IdentitySet to Set and IdentityDictionary to Map, but this is not a priority.

The image is serialized sort of like a JavaScript storeString. No processes or contexts though, or rather they are not brought back in on the JavaScript side. Blocks are both stored and loaded.

Non-local returns, unwind blocks, resumable and restartable exceptions are implemented via JavaScript exception handling plus explicit handler block chains associated with the processes.

The "image" starts with the global state loaded, but all processes are started from scratch instead of resumed. A non-UI image is thus trivially started.

One major todo left is hooking up the UI/browser. I did take vm.display.browser.js from SqueakJS and adapted the code in order to implement its numbered primitives, but I still have to work through squeak.js from the same to initialize 
and hook up the display.

Florin