better overflow check

Author: jquense

src/ModalManager.js

@@ -1,14 +1,7 @@
 import css from 'dom-helpers/style';
 import classes from 'dom-helpers/class';
 import getScrollbarSize from 'dom-helpers/util/scrollbarSize';
-import isWindow from 'dom-helpers/query/isWindow';
-
-function containerClientHeight(container) {
-  let win = isWindow(container);
-  return win
-      ? win.documentElement.clientHeight
-      : container.clientHeight;
-}
+import isOverflowing from './utils/isOverflowing';
 
 let findContainer = (data, modal)=> {
   let idx = -1;
@@ -73,7 +66,7 @@ class ModalManager {
       overflow: 'hidden'
     };
 
-    data.overflowing = container.scrollHeight > containerClientHeight(container);
+    data.overflowing = isOverflowing(container);
 
     if (data.overflowing) {
       // use computed style, here to get the real padding

src/utils/isOverflowing.js

@@ -0,0 +1,28 @@
+import isWindow from 'dom-helpers/query/isWindow';
+import ownerDocument from 'dom-helpers/ownerDocument';
+
+function isBody(node){
+  return node && node.tagName.toLowerCase() === 'body';
+}
+
+function bodyIsOverflowing(node){
+  let doc = ownerDocument(node);
+  let win = isWindow(doc);
+  let fullWidth = win.innerWidth;
+
+  // Support: ie8, no innerWidth
+  if (!fullWidth) {
+    let documentElementRect = doc.documentElement.getBoundingClientRect();
+    fullWidth = documentElementRect.right - Math.abs(documentElementRect.left);
+  }
+
+  return doc.body.clientWidth < fullWidth;
+}
+
+export default function isOverflowing(container) {
+  let win = isWindow(container);
+
+  return win || isBody(container)
+      ? bodyIsOverflowing(container)
+      : container.scrollHeight > container.clientHeight;
+}