A Smalltalk virtual machine written in pure JavaScript, running real .image files in a
browser tab — no plugin, no server doing the work. Live at smalltalkjsvm.com.ar.
This is a fork of SqueakJS, written by Vanessa Freudenberg, who showed a decade ago that a full Smalltalk VM could live in a web page. The interpreter, the object memories, BitBlt and the plugin machinery are hers; everything below is what this fork adds on top.
Pharo runs here. Versions 10 through 13, 32- and 64-bit, boot to a clean, interactive
world — including the image the Pharo Launcher installs today. That took a dozen VM fixes
(64-bit indexable arrays, the Sista push thisProcess bytecode, file-attribute and
working-directory primitives, semaphores that accept subclasses, a wordSize that 64-bit
Pharo reads from a class variable) plus startup scripts that give the 64-bit builds back the
display and event classes they dropped when they moved to SDL2. See pharo/README.md
for how those work and how the Morphic demo image is built.
Cuis 7.x runs here, once the VM learned the 16- and 64-bit array formats the newer images
use, gained primitiveGet/SetWorkingDirectory, and started falling back to the plain
interpreter when the JIT hits a bytecode it mishandles instead of killing the image.
A Web Worker runtime. squeak_worker.js runs the VM off the main thread, drawing on an
OffscreenCanvas, so the page keeps answering while the image works. It carries the pieces a
worker has no access to on its own: the file system's directory listing is passed in from the
host, saved images come back out to Downloads, and input, cursor, clipboard, sound, resize and
drag-and-drop are forwarded both ways. See WORKER.md.
A launcher that fits the image to the VM. run/index.html reads a dropped .image
to see which Pharo compatibility script it needs and installs it, downloads bundles and
multi-file image sets, and clears a startup script left behind by a previous run so it cannot
leak into the next image.
The site. utils/mk-site.py builds the standalone tree published at smalltalkjsvm.com.ar: the launcher, exactly the VM modules it imports, and the compatibility scripts. No image is hosted — every example links the build its own project publishes, through a small CORS worker for the two servers that send no CORS headers.
In a browser. Serve the repository and open run/:
npx serve # or: npm start
then drag a Smalltalk image onto the page (with its .changes and .sources if it has them),
or pick one of the examples. A local web server is needed because images are loaded with
fetch, which does not work from a file: URL.
From the command line. node squeak_node.js headless/headless.image — add -ignoreQuit
to stop the image quitting when it finds no display.
Bundled. dist/squeak_bundle.js and dist/squeak_headless_bundle.js are single-file
builds for pages that cannot use ES modules; npm run build regenerates them.
There is no bundler for the core VM. globals.js installs a small Lively-Kernel-style class
system — Object.subclass('Squeak.Foo', {...}) and Object.extend(target, {...}) — and the
entry points load the pieces in an order that matters:
vm.js |
the Squeak namespace: object header layout, special-object indices, module registry |
vm.object.js, vm.object.spur.js |
the two object memory representations; Spur images use the second |
vm.image.js |
parses a raw .image into a live object graph, old and Spur/64-bit formats |
vm.interpreter.js |
the bytecode interpreter; interpret(ms, thenDo) is driven from outside so it never blocks the event loop |
vm.primitives.js |
built-in primitives and the dispatcher that loads plugins by name |
jit.js |
optional JIT — it removes bytecode-decode overhead, it does not optimize |
vm.display.*, vm.input.*, vm.files.browser.js |
platform backends, browser and headless variants |
Plugins come in two kinds, both registered with Squeak.registerExternalModule: the
hand-written internal ones (vm.plugins.*.js) and the external ones in plugins/, most of
which are generated from Smalltalk VMMaker source by the code generator in
utils/VMMakerJS.package — those carry a header naming their generator, and fixing a bug in
one means fixing the Smalltalk source and regenerating, not patching the JavaScript.
Bug reports and pull requests welcome. Fixes that belong to the engine itself are better sent upstream, where they help everyone using SqueakJS.
SqueakJS is by Vanessa Freudenberg (codefrau) and its contributors; the engine's own history is in the upstream changelog. The Pharo and Cuis 7.x compatibility work, the Web Worker runtime and the launcher in this fork are by Agustín Martínez. MIT licensed, like the original — see LICENSE.md.