PCjs Machines

Home of the original IBM PC emulator for browsers.


PCjs Blog

Completing the Switch to ES6 Classes

As I mentioned last December, I had started converting PCjs machines to ECMAScript 2015, more conveniently known as ES6. At the time, only one PCjs machine, PDPjs, had been converted, which left the website in the unfortunate position of having duplicate shared modules: one set for ES5-based machines and another set for ES6.

Well, I’m happy to report that today marks the completion of the ES6 conversion, and the return of a single set of shared modules.

Admittedly, I was dragging my feet a bit, because the largest and most complex machine emulator, PCx86, was going to require a fair bit work, not to mention regression testing. However, after converting three other PCjs machines (PDP11, PCx80, and C1Pjs), I had become pretty proficient at the conversion, so I was able to bulldoze my way through all the PCx86 files in a few hours, and fixing all the Closure Compiler compilation errors only took another hour or so.

It’s hard to say whether the conversion was really worth the effort, since I’m still using the Closure Compiler to transpile the code back to ES5. Also, since two of the emulators (PCx86 and PDP11) can also be launched from the Node command-line, I’ve adopted Node’s require() convention for importing the other scripts as modules, which makes them difficult to load inside a web browser if you want to test or debug the uncompiled code.

To resolve that, I updated the built-in Node web server to “magically” strip out all the Node-specific stuff before serving up the individual JavaScript files. Eventually, I’ll change the Node server’s page template to use <script type="module" .../> instead of <script type="text/javascript" .../>, but that won’t happen until all web browsers support module loading AND Node fully supports import and export instead of require() and module.exports.

I do like the new ES6 class syntax much more than the old prototype-based syntax. We’ve gone from JavaScript classes that were like “lipstick on a pig” to classes that are more like “lipstick on a piglet” – still a pig, but much cuter.

For years, JavaScript fans have been trying to convince us that “prototypal inheritance” was better and more powerful than traditional class-based inheritance models. As far as I’m concerned, object prototypes were a hack, and no amount of after-the-fact rationalizations will convince me that they were actually a thoughtfully designed feature of the language. Not to mention the fact that prototype-based classes are tedious to write and unpleasant to look at.

Obviously, I was not alone, because we now have ES6 classes.

Do I still have gripes? Sure. My biggest grumble is that I can’t easily define class constants; I have to attach them to the class after I finish defining the class, and even then, I can’t declare them as const. I guess there are ways to do it, such as:

Object.defineProperty(SampleClass, 'ANSWER', {
	value: 42,
	writable : false,
	enumerable : true,
	configurable : false

But who in their right mind is going to write all that just to define a single numeric class constant? I would love to be able to add a class constant inside a class with a simple:

static const ANSWER = 42;

Beyond ES6 classes, there are several other improvements I’d like to make to the PCjs code base, including more extensive use of:

Those changes will come, but on a more piecemeal basis, as code is visited.

Jeff Parsons
Jan 31, 2017