docs: cleanup after requestAnimationFrame example

docs/src/pages/blog/anywidget-02.md

@@ -215,6 +215,31 @@ export default { render };
 > Note: The above front-end code requires transformation with tool like
 > `esbuild` to allow for the special JSX syntax (e.g., `<App />`).
 
+Another common scenario requiring proper cleanup is when using
+`requestAnimationFrame` to continually redraw into a canvas:
+
+```javascript
+export default {
+	render({ model, el }) {
+		const canvasEl = document.createElement("canvas");
+		let requestId = requestAnimationFrame(step);
+
+		function step() {
+			/* ...custom rendering goes here... */
+			requestId = requestAnimationFrame(step);
+		}
+		el.appendChild(canvasEl);
+
+		return () => {
+			cancelAnimationFrame(requestId);
+		};
+	},
+};
+```
+
+This prevents the accumulation of several animation loops executing at the same
+time after re-running the cell a bunch of times.
+
 ## Getting Started
 
 To start using **anywidget** v0.2, upgrade your package using pip: