Use basic fallback for document.scrollingElement (#15)

* Update version and tags.

* Use basic fallback for `document.scrollingElement`.

* Update `README.md`.

README.md

@@ -40,6 +40,27 @@ https://caniuse.com/#feat=mdn-api_htmlelement_focus_preventscroll_option
   https://bugs.webkit.org/show_bug.cgi?id=178583
 
 
+## document.scrollingElement
+
+This polyfill uses a basic fallback for the [document.scrollingElement](https://developer.mozilla.org/en-US/docs/Web/API/Document/scrollingElement) property, using `document.documentElement` when not found.
+
+This could suffice in basic cases, but if you need wider and/or specific support you should refer to a polyfill for it:
+
+* https://github.com/mathiasbynens/document.scrollingElement
+
+Also, to overcome its absence if you are executing this polyfill through [`jsdom`](https://github.com/jsdom/jsdom), you could place this in your setup:
+
+```js
+document.scrollingElement = document.documentElement
+```
+
+More context about this property can be found in:
+
+* https://developer.mozilla.org/en-US/docs/Web/API/Document/scrollingElement
+* https://developer.mozilla.org/en-US/docs/Web/HTML/Quirks_Mode_and_Standards_Mode
+* https://developer.mozilla.org/en-US/docs/Web/API/Document/documentElement
+
+
 ## Dev and testing
 
 To check this polyfill you can do:

index.js

@@ -37,8 +37,10 @@
     var calcScrollableElements = function(element) {
       var parent = element.parentNode;
       var scrollableElements = [];
+      var rootScrollingElement =
+        document.scrollingElement || document.documentElement;
 
-      while (parent && parent !== document.scrollingElement) {
+      while (parent && parent !== rootScrollingElement) {
         if (
           parent.offsetHeight < parent.scrollHeight ||
           parent.offsetWidth < parent.scrollWidth
@@ -51,7 +53,7 @@
         }
         parent = parent.parentNode;
       }
-      parent = document.scrollingElement;
+      parent = rootScrollingElement;
       scrollableElements.push([parent, parent.scrollTop, parent.scrollLeft]);
 
       return scrollableElements;

package.json

@@ -1,6 +1,6 @@
 {
   "name": "focus-options-polyfill",
-  "version": "1.3.0",
+  "version": "1.4.0",
   "description": "JavaScript polyfill for the WHATWG spec of focusOptions, that enables a set of options to be passed to the focus method.",
   "main": "index.js",
   "scripts": {
@@ -16,6 +16,9 @@
     "polyfill",
     "javascript-polyfill",
     "focus",
+    "options",
+    "focusOptions",
+    "preventScroll",
     "whatwg",
     "whatwg-dom",
     "js"