fix(framework): adapt ie11 package for usage in modern browsers (#2878)

Author: fifoosid

packages/base/src/DOMObserver.js

@@ -21,15 +21,19 @@ let _destroyObserver = observer => {
  * @param createFn
  */
 const setCreateObserverCallback = createFn => {
-	_createObserver = createFn;
+	if (typeof createFn === "function") {
+		_createObserver = createFn;
+	}
 };
 
 /**
  * Allows to create an alternative DOM observer implementation
  * @param destroyFn
  */
 const setDestroyObserverCallback = destroyFn => {
-	_destroyObserver = destroyFn;
+	if (typeof destroyFn === "function") {
+		_destroyObserver = destroyFn;
+	}
 };
 
 /**

packages/ie11/src/integrate.js

@@ -18,8 +18,10 @@ attachThemeLoaded(runPonyfill);
 attachBeforeComponentRender(createComponentStyleTag);
 
 // Set the custom DOM observer implementation for observe/unobserve
-setCreateObserverCallback(window.ShadyDOM.observeChildren);
-setDestroyObserverCallback(window.ShadyDOM.unobserveChildren);
+const observeChildrenMethod = window.ShadyDOM ? window.ShadyDOM.observeChildren : undefined;
+const unobserveChildrenMethod = window.ShadyDOM ? window.ShadyDOM.unobserveChildren : undefined;
+setCreateObserverCallback(observeChildrenMethod);
+setDestroyObserverCallback(unobserveChildrenMethod);
 
 // Set the custom Resize observer implementation for observe/unobserve
 setResizeHandlerObserveFn(customObserve);