SqueakJS changes its world with ThisWebpage

a new platform

Since becoming a virtual-machine-based app, Smalltalk has integrated well with other operating systems, providing the illusion of a consistent unified platform. With the ascendancy of JavaScript, the common execution environment provided by web browsers is effectively another host operating system. Smalltalk runs there too now, thanks to Bert Freudenberg’s SqueakJS. So in addition to macOS, Windows, and Linux, we now have the Web host platform.

While all platforms expose some of their functionality to apps through system calls, the Web exposes much more, through its Document Object Model API (DOM). This gives Smalltalk a special opportunity to enable livecoded apps on this platform. It also means that Smalltalk can interoperate more extensively with other Web platform apps, and participate in the ecosystem of JavaScript frameworks, both as a consumer and a producer.

to JavaScript and back

The part of SqueakJS which enables this is its bidirectional JavaScript bridge. This is implemented by class JSObjectProxy, and some special support in the SqueakJS virtual machine. One may set Smalltalk variables to JavaScript objects, send messages to JavaScript objects, and provide Smalltalk block closures as callback functions to JavaScript. One may interact with any JavaScript object in the Web environment. This means we can manipulate DOM objects as any other JavaScript framework would, to create new HTML5 user interfaces and modify existing ones.

In particular, we can embed SqueakJS in a web page, and modify that web page from SqueakJS processes. It would be very useful to have a Smalltalk object model of the host web page. I have created such a thing with the new class ThisWebpage.

reaching out with ThisWebpage

I chose the name of ThisWebpage to be reminiscent of “thisContext”, the traditional Smalltalk pseudo-variable used by an expression to access its method execution context. In a similar way, expressions can use ThisWebpage to access the DOM of the hosting Web environment. One simple example is adding a button:

ThisWebpage
  createButtonLabeled: 'fullscreen'
  evaluating: [Project current fullscreen: true]

Behind the scenes, ThisWebpage is doing this:

(JS document createElement: 'input')
  at: #type
  put: 'button';
  at: #onclick:
  put: [Project current fullscreen: true]

Class JSObjectProxy creates JS, an instance of itself, during installation of the JavaScript bridge. It corresponds to the JavaScript DOM object for the current web browser window, the top of the DOM object graph. By sending createElement:, the expression is invoking one of the DOM methods. The entire set of DOM methods is well-documented online (for example, here’s the documentation for Document.createElement).

So far, ThisWebpage has some basic behavior for adding buttons and frames, and for referring to the document elements in which SqueakJS is embedded. It can also create links and synthesize clicks on them. This is an important ability, which I use in making a Squeak object memory jump from SqueakJS in a web browser to a native Cog virtual machine on the desktop (the subject of tomorrow’s post).

The possibilities here are immense. ThisWebpage is waiting for you to make it do amazing front-end things! Check it out as part of the Context 7 alpha 1 release.

 

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6 Responses to “SqueakJS changes its world with ThisWebpage”

  1. Milt Latta Says:

    Yay, Craig! Looks like it’s released. I don’t understand the details but it seems pretty powerful and useful to me. Best wishes for lots of response.

  2. Interesting.
    One would then start wrapping other APIa like the history and local storage ones.
    This would be endless as we have a lot of them…

  3. Hari Balaraman Says:

    [NewbieQuestion] Craig, This looks amazing. I am particularly impressed by the responsiveness of the UI of the image you are displaying. I have been testing a small app running on a Cuis image on SqueakJS on a local webserver (which shouldn’t be too intensive a workload in terms of ) and I find that my mouse disappears. At the risk of asking a too-short question that needs a too-long answer, what is the difference between your implementation and Bert’s instructions serving up squeakjs in an html file using a webserver? (I’m wondering what I need to do to make my damn mouse pointer to reappear)

  4. […] « SqueakJS changes its world with ThisWebpage […]

  5. […] that we’ve seen how to run Smalltalk in a web browser, clone web Smalltalk as a desktop app, and send remote messages between Smalltalks, let’s […]

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