For the impatient… here it is.
Back to the Future, Again
With the arrival of Bert Freudenberg’s SqueakJS, it was finally time for me to revisit the weird and wonderful world of JavaScript and web development. My previous experiences with it, in my consulting work, were marked by awkward development tools, chaotic frameworks, and scattered documentation. Since I ultimately rely on debuggers to make sense of things, my first question when evaluating a development environment is “What is debugging like?”
Since I’m a livecoder, I want my debugger to run in the web browser I’m using to view the site I’m debugging. The best in-browser debugger I’ve found, Chrome DevTools (CDT), is decent if you’re used to a command-line interface, but lacking as a GUI. With Smalltalk, I can open new windows to inspect objects, and keep them around as those objects evolve. CDT has an object explorer integrated into its read-eval-print loop (REPL), and a separate tab for inspecting DOM trees, but using them extensively means a lot of scrolling in the REPL (since asynchronous console messages show up there as well) and switching between tabs. CDT can fit compactly onto the screen with the subject website, but doesn’t make good use of real estate when it has more. This interrupts the flow of debugging and slows down development.
The Pieces Are All Here
With SqueakJS, and its JavaScript bridge, we can make something better. We can make an in-browser development environment that compares favorably with external environments like WebStorm. I started from a page like try.squeak.org. The first thing we need is a way to move the main SqueakJS HTML5 canvas around the page. I found jQuery UI to be good for this, with its “draggable” effect. While we’re at it, we can also put each of Squeak‘s Morphic windows onto a separate draggable canvas. This moves a lot of the computation burden from SqueakJS to the web browser, since SqueakJS no longer has to do window management. This is a big deal, since Morphic window management is the main thing making modern Squeak UIs feel slow in SqueakJS today.
SqueakJS provides a basic proxy class for JavaScript objects, called JSObjectProxy. Caffeine has an additional proxy class called JSObject, which provides additional reflection features, like enumerating the subject JS object’s properties. It’s also a good place for documenting the behavior of the JS objects you’re using. Rather than always hunting down the docs for HTMLCanvasElement.getContext on MDN, you can summarize things in a normal method comment, in your HTMLCanvasElement class in Smalltalk.
Multiple Worlds
With a basic window system based on HTML5 canvases, we can draw whatever we like on those canvases, using the SqueakJS bridge and whatever other JS frameworks we care to load. I’ve started integrating a few frameworks, including React (for single-page-app development), three.js (for WebGL 3D graphics development), and morphic.js (a standalone implementation of Morphic which is faster than what’s currently in Squeak). I’ll write about using them from Caffeine in future blog posts.
Another framework I’ve integrated into Caffeine is Snowglobe (for Smalltalk app streaming and other remote GUI access), which I wrote about here previously. I think the Snowglobe demo is a lot more compelling when run from Caffeine, since it can co-exist with other web apps in the same page. You can also run multiple Snowglobes easily, and drag things between them. I’ll write more about that, too.
Fitting Into the JavaScript Ecosystem
To get the full-featured debugger UI I wanted, I wrote a Chrome extension called Caffeine Helper, currently available on the Chrome Web Store. It exposes the Chrome Debugging Protocol (CDP) support in the web browser to SqueakJS, letting it do whatever the CDT can do (CDT, like SqueakJS, is just another JavaScript-powered web app). The support for CDP that I wrote about previously uses a WebSocket-based CDP API that requires Chrome to be started in a special way. The Caffeine Helper extension provides a JavaScript API, without that requirement.
I also wrote support for generating Smalltalk code from JavaScript, using the esprima parsing framework, and vice-versa. With my debugger and code generation, I’m going to try developing for some file-based JS projects, using Smalltalk behind the scenes and converting to and from JavaScript when necessary. I think JS web development might actually not drive me crazy this way. :)
Please Try It Out!
So, please check out Caffeine, at caffeine.js.org! I would very much appreciate your feedback. I’m particularly interested to hear your use cases, as I plan the next development steps. I would love to have collaborators, too. Let’s build!
