Merge pull request #201 from alice/bodyScroll

Don't need to take container scroll into account if container is body

Changelog.md

diff --git a/Changelog.md b/Changelog.md
index 604fe5d..2d1ebcf 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -14,6 +14,7 @@
 * Revert #150 which was causing the extension not to work.
 * AX_HTML_02 (duplicate IDs) now only audits elements that are referenced by an IDREF (#141);
 * Fix #171 by being smarter about finding the composed parent node.
+* Tweak in canScrollTo to handle the (common) case where the container is `document.body` (#243).
 
 ## 2.9.0 - 2015-09-04
 
@@ -127,4 +128,4 @@
 
 * axs.utils.isLowContrast() now rounds to the nearest 0.1 before checking (so `#777` is now a passing value)
 * MainRoleOnInappropriateElement was always failing due to accessible name calculation taking the main role into account and not descending into content (now just gets descendant content directly)
-* UnfocusableElementsWithOnClick had a dangling if-statement causing very noisy false positives
\ No newline at end of file
+* UnfocusableElementsWithOnClick had a dangling if-statement causing very noisy false positives

src/js/AccessibilityUtils.js

diff --git a/src/js/AccessibilityUtils.js b/src/js/AccessibilityUtils.js
index 3466133..657348a 100644
--- a/src/js/AccessibilityUtils.js
+++ b/src/js/AccessibilityUtils.js
@@ -103,16 +103,21 @@
 axs.utils.canScrollTo = function(element, container) {
     var rect = element.getBoundingClientRect();
     var containerRect = container.getBoundingClientRect();
-    var containerTop = containerRect.top;
-    var containerLeft = containerRect.left;
+    if (container == container.ownerDocument.body) {
+        var absoluteTop = containerRect.top;
+        var absoluteLeft = containerRect.left;
+    } else {
+        var absoluteTop = containerRect.top - container.scrollTop;
+        var absoluteLeft = containerRect.left - container.scrollLeft;
+    }
     var containerScrollArea =
-        { top: containerTop - container.scrollTop,
-          bottom: containerTop - container.scrollTop + container.scrollHeight,
-          left: containerLeft - container.scrollLeft,
-          right: containerLeft - container.scrollLeft + container.scrollWidth };
+        { top: absoluteTop,
+          bottom: absoluteTop + container.scrollHeight,
+          left: absoluteLeft,
+          right: absoluteLeft + container.scrollWidth };
 
     if (rect.right < containerScrollArea.left || rect.bottom < containerScrollArea.top ||
-            rect.left > containerScrollArea.right || rect.top > containerScrollArea.bottom) {
+        rect.left > containerScrollArea.right || rect.top > containerScrollArea.bottom) {
         return false;
     }