Don't shadow global document/window, and fall back on them.

Author: RobRendell

src/index.tsx

@@ -44,15 +44,15 @@ type AnyPortalNode<C extends Component<any> = Component<any>> = HtmlPortalNode<C
 
 
 const validateElementType = (domElement: Element, elementType: ANY_ELEMENT_TYPE) => {
-    const document = domElement.ownerDocument as any;
+    const ownerDocument = (domElement.ownerDocument ?? document) as any;
     // Cast document to `any` because Typescript doesn't know about the legacy `Document.parentWindow` field, and also
     // doesn't believe `Window.HTMLElement`/`Window.SVGElement` can be used in instanceof tests.
-    const window = document.defaultView ?? document.parentWindow; // Fallback on `parentWindow` in order to support IE8 and earlier
+    const ownerWindow = ownerDocument.defaultView ?? ownerDocument.parentWindow ?? window; // `parentWindow` for IE8 and earlier
     if (elementType === ELEMENT_TYPE_HTML) {
-        return domElement instanceof window.HTMLElement;
+        return domElement instanceof ownerWindow.HTMLElement;
     }
     if (elementType === ELEMENT_TYPE_SVG) {
-        return domElement instanceof window.SVGElement;
+        return domElement instanceof ownerWindow.SVGElement;
     }
     throw new Error(`Unrecognized element type "${elementType}" for validateElementType.`);
 };