`Cannot read properties of undefined (reading 'element')` during cleanup

[kirbysayshi]

Description

Occasionally, when tearing down via rive-react's useRive hook, we're seeing an error in rive-wasm / canvas:

Cannot read properties of undefined (reading 'element') (see screenshot of stack track below)

Provide a Repro

I don't have a repro, but I do have a stacktrace from our Sentry instance:

This clearly shows that observed is undefined.

Our usage is extremely simple:

function CorrectAnimation() {
  const { RiveComponent, rive } = useRive({
    src: getStaticAssetPath('anims/correct-animation.riv'),
    autoplay: true,
    layout: new Layout({ fit: Fit.Cover, alignment: Alignment.TopCenter }),
  });

  return <RiveComponent />;
}

Browser & Versions

• Browser: Chrome 130, Firefox 131 (we've seen the error in both)
• OS: macOS 10.15
• pnpm -v: 9.5.0
• @rive-app/react-canvas 4.15.2
• @rive-app/canvas 2.22.0

Additional context

What I believe is happening:

There is a null check here:

rive-wasm/js/src/rive.ts

Lines 2104 to 2106 in 9138225

	if (this._observed !== null) {
	observers.remove(this._observed);
	}

But not an undefined check, resulting in observed being undefined and then erroring out when observed.element is attempted to be resolved.

As to why observed is undefined, I am not sure. I see that it's conditionally initialized in the constructor... although I don't quite understand how that condition could be false.

rive-wasm/js/src/rive.ts

Lines 1564 to 1569 in 9138225

	if (params.canvas.constructor === HTMLCanvasElement) {
	this._observed = observers.add(
	this.canvas as HTMLCanvasElement,
	this.onCanvasResize,
	);
	}

One straightforward fix might simply be initializing it to null here (but this does not answer why):

rive-wasm/js/src/rive.ts

Lines 1491 to 1492 in 9138225

	// Reference of an object that handles any observers for the animation
	private _observed: ObservedObject | null;

[kirbysayshi]

I'd also like to report that applying the fix from #376 via a local pnpm patch fixed the errors! So it would be great to get that merged.