[screenshotter] add comments

Author: Xiaoyu Yin

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@sigmacomputing/plugin",
-  "version": "1.0.3",
+  "version": "1.0.5",
   "description": "Sigma Computing Plugin Client API",
   "license": "MIT",
   "homepage": "https://github.com/sigmacomputing/plugin",

src/index.ts

@@ -2,4 +2,4 @@ export * from './types';
 export * from './react';
 export * from './client';
 
-export * from './utils/requestAnimationFramePolyfill';
+export {polyfillRequestAnimationFrame} from './utils/polyfillRequestAnimationFrame';

src/utils/polyfillRequestAnimationFrame.ts

@@ -0,0 +1,12 @@
+/**
+ * requestAnimationFrame() calls are paused in most browsers when running in background tabs or hidden <iframe>s in order to improve performance and battery life
+ * 
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame
+ * @param w Window Object
+ */
+export function polyfillRequestAnimationFrame(w: Window) {
+  if ('requestAnimationFrame' in w) {
+    w.requestAnimationFrame = cb => w.setTimeout(cb, 1000 / 60);
+    w.cancelAnimationFrame = id => w.clearTimeout(id);
+  }
+}