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SqueakJS: A Squeak VM for the Web and Node.js

SqueakJS is an HTML5 runtime engine for Squeak Smalltalk written in pure JavaScript. It also works for many other OpenSmalltalk-compatible images.

Embedding a Smalltalk application in your webpage can be as simple as:

SqueakJS.runSqueak(imageUrl, canvas);

The interpreter core is divided in a number of vm.*.js modules, internal plugins in vm.plugins.*.js modules and external plugins in the "plugins" directory. The Just-in-Time compiler is optional ("jit.js") and can be easily replaced with your own.

There are a number of interfaces:

  • browser: the regular HTML interface lets you use SqueakJS on your own web page. Just include "squeak.js".
  • headless browser: a headless VM. It lets you use SqueakJS in your browser without a direct UI (you can create your own UI with a plugin). Include "squeak_headless.js" and add an "imageName" parameter to your website URL (eg. or call the Javascript function "fetchImageAndRun('')" to start the specified image.
  • Node.js: another headless VM. It lets you use SqueakJS as a Node.js application. Just run "node squeak_node.js ".

For discussions, please use the vm-dev mailing list. Also, please visit the project home page!

Running it


  • Run a minimal image. This is the simple demo included in this repo.
  • Or run Etoys. Everything except the image and template files is in this repo.
  • Or similarly, Scratch, also in here.

Run your own Squeak image in the browser

  • Drag an image from your local files into the launcher.
  • ... and all the other demo pages (see above) accept dropped images, too.

Run your own Squeak image from the command line

  • Install a recent version of Node.js
  • Run example image: node squeak_node.js headless/headless.image

Run an interactive shell based on WebSocket communication with Cuis image

  • Install a recent version of Node.js
  • Go to ws and execute in a first shell and in a second shell.
  • After initialization it should be possible to issue Smalltalk statements which will be executed in the Smalltalk image.
  • Try commands like: Object allSubclasses size 1837468731248764723 * 321653125376153761 Collection allSubclasses collect: [ :c | c name ]

Which Browser

All modern browsers should work (Chrome, Safari, IE, FireFox), though Chrome performs best currently. Safari on iPad works somewhat. YMMV. Fixes to improve browser compatibility are highly welcome!

If your browser does not support ES6 modules try the full or headless SqueakJS VM as a single file (aka bundle) in the Distribution directory.

Installing locally

  • clone the github repo:

    git clone

    or download and unpack the ZIP archive

  • serve the SqueakJS directory using a local web server.

    TIP: If you have Node.js, try

    cd SqueakJS
    npx serve

    which will run a webserver on port 3000.

  • in a web browser, open http://localhost:3000/run/ and pick one of the images, or drag and drop your own

Now Squeak should be running. The reason for having to run from a web server is because the image is loaded with an XMLHttpRequest which does not work with a file URL. Alternatively, you could just open SqueakJS/run/index.html and drop in a local image.

Using (self contained) bundled files

  • select your preferred type of interface (browser or headless)
  • use the appropriate file (squeak_bundle.js resp. squeak_headless_bundle.js) from the Distribution directory
  • you can also build minified bundles using npm run build

How to modify it

  • use any text editor
  • you have to reload the page for your changes to take effect

How to share your changes

  • easiest for me is if you create a pull request
  • otherwise, send me patches

Contributions are very welcome!

Things to work on

SqueakJS is intended to run any Squeak image. It can already load any image from the original 1996 Squeak release to the latest Cog-Spur release, including 64-bit and Sista variants. But various pieces (primitives in various plugins) are still missing, in particular 3D graphics and networking (however, see Croquet which supports both, but should be generalized). Also, we should make pre-Spur 64 bit images load. And, it would be nice to make it work on as many browsers as possible, especially on mobile touch devices.

As for optimizing I think the way to go is an optimizing JIT compiler. The current JIT is very simple and does not optimize at all. Since we can't access or manipulate the JavaScript stack, we might want that compiler to inline as much as possible, but keep the call sequence flat so we can return to the browser at any time. Even better (but potentially more complicated) is actually using the JavaScript stack, just like Eliot's Stack VM uses the C stack. I have done some advanced JIT mockups. To make BitBlt fast, we could probably use WASM or even WebGL.

To make SqueakJS useful beyond running existing Squeak images, we should use the JavaScript bridge to write a native HTML UI which would certainly be much faster than BitBlt.

Better Networking would be interesting, too. The SocketPlugin currently does allows HTTP(S) requests and WebSockets. How about implementing low level Socket support based on HTTP-tunneling? The VM can run in a WebWorker. How about parallelizing the VM with WebWorkers?

There's a gazillion exciting things to do :)

-- Vanessa Freudenberg (codefrau)


2024-06-22: 1.2.2 make copy/paste work on mobile
2024-05-27: 1.2.1 add virtual cmd button, fix touch events
2024-03-25: 1.2.0 add FFI and MIDI plugins, JIT for Sista bytecodes, JPEG write prim, fix keyboard input, copy/paste, scroll wheel, highdpi, allow ES6 in source
2023-11-24: 1.1.2 fixed BitBlt bug (symptom reported 9 years ago, thanks to Agustin Martinez for narrowing it down), add object pinning, support keyboard in ancient Scratch images
2023-10-24: 1.1.1 workarounds for Cuis 6
2023-10-23: 1.1.0 implement Etoys project saving (image segment export), drag-n-drop directories
2023-09-30: 1.0.6 fixes
2022-11-19: 1.0.5 fixes, add highdpi mode, add image format for Squeak 6
2021-05-31: 1.0.4 fixes
2021-03-21: 1.0.3 headless fixes (Erik Stel); fixes object-as-method
2021-02-07: 1.0.2 new one-way become prim (Christoph Tiede); JIT-compile Array at:/at:put:
2021-01-05: 1.0.1 fixes some primitives to properly pop the stack
2020-12-20: 1.0 supports 64 bits and Sista
2020-06-20: renamed "master" branch to "main"
2020-06-20: 0.9.9 JSBridge additions (Bill Burdick), fixes
2020-04-08: renamed github account to "codefrau"
2020-01-26: 0.9.8 split into modules (Erik Stel), fixes
2019-01-03: 0.9.7 minor fixes
2018-03-13: 0.9.6 minor fixes
2016-11-08: 0.9.5 more fixes
2016-10-20: 0.9.4 fixes
2016-09-08: 0.9.3 add partial GC (5x faster become / allInstances)
2016-08-25: 0.9.2 add keyboard on iOS
2016-08-03: 0.9.1 fixes
2016-07-29: 0.9 Spur support, stdout, SpeechPlugin, zipped images
2016-06-28: 0.8.3 add SocketPlugin for http/https connections
2016-04-07: 0.8.2 better touch handling, debugging, CORS, lint
2016-01-08: 0.8.1 windows keyboard fixes, 'new' operator fixed
2015-11-24: 0.8 minor fixes
2015-08-13: 0.7.9 make work on iOS again
2015-07-18: 0.7.8 fix keyboard
2015-06-09: 0.7.7 fix thisContext
2015-04-27: 0.7.6 revert JIT, minor fixes
2015-04-14: 0.7.5 JIT optimizations by HPI students (reverted in 0.7.6)
2015-02-18: 0.7.4 make pre-release image work
2015-01-30: 0.7.3 JSBridge: fix closure callbacks
2015-01-25: 0.7.2 JSBridge: add asJSObject
2014-12-22: 0.7.1 cursor shapes
2014-12-04: 0.7 support finalization of weak references
2014-11-28: 0.6.8 JSBridge with callbacks
2014-11-20: 0.6.7 implement JavaScriptPlugin
2014-11-18: 0.6.6 implement DropPlugin
2014-11-14: 0.6.5 add generated Balloon2D plugin
2014-11-06: 0.6.4 add generic run page
2014-10-28: 0.6.3 pass options via URL
2014-10-27: add JPEG plugin
2014-10-25: add template files
2014-10-23: 0.6.2 fixes
2014-10-21: 0.6.1 add image segment loading
2014-10-18: 0.6 move squeak.js out of lib dir
2014-10-13: 0.5.9 microphone support
2014-10-09: 0.5.8 fixes
2014-10-07: 0.5.7 even more plugins generated
2014-10-07: 0.5.6 add quitSqueak and onQuit
2014-10-07: 0.5.5 generated ScratchPlugin
2014-10-06: 0.5.4 replace BitBltPlugin by generated
2014-10-06: 0.5.3 SoundGenerationPlugin, Matrix2x3Plugin, FloatArrayPlugin
2014-10-05: ZipPlugin
2014-10-04: MiscPrimitivePlugin
2014-10-03: VMMakerJS generates LargeIntegersPlugin
2014-09-30: 0.5.2 more JIT
2014-09-28: 0.5.1 JIT fixes
2014-09-26: 0.5 add JIT compiler
2014-09-22: v8 optimizations
2014-09-20: 0.4.6 sound output support
2014-09-13: 0.4.5 clipboartd fixes
2014-09-12: 0.4.4 cut/copy/paste in stand-alone
2014-09-09: 0.4.3 some scratch prims
2014-09-09: 0.4.2 idle fixes
2014-09-05: 0.4.1 scratch fixes
2014-09-04: 0.4.0 runs scratch
2014-08-31: switch old/new primitives
2014-08-27: event-based input
2014-08-21: exception handling
2014-07-25: 0.3.3 fullscreen support
2014-07-18: 0.3.2 benchmarking (timfel)
2014-07-18: 0.3.1 deferred display
2014-07-16: 0.3.0 closure support
2014-07-14: 0.2.3 IE optimization (timfel)
2014-07-11: 0.2.2 drag-n-drop
2014-07-07: 0.2.1 fixes for IE11 (timfel)
2014-07-04: 0.2 runs Etoys
2014-06-27: Balloon2D (krono)
2014-06-03: stand-alone version
2014-05-29: 0.1 added version number
2014-05-27: WarpBlt
2014-05-07: image saving
2014-04-23: file support
2013-12-20: public release
2013-12-14: colored bitblt
2013-12-03: first pixels on screen
2013-11-29: GC
2013-11-22: runs 43 byte codes and 8 sends successfully
2013-11-07: initial commit