Ensure descendantOf doesn’t try to compare an element with a non-element. [close prototypejs#152]

Author: savetheclocktower

src/prototype/dom/dom.js

@@ -2137,20 +2137,23 @@
   **/
   function descendantOf_DOM(element, ancestor) {
     element = $(element), ancestor = $(ancestor);
+    if (!element || !ancestor) return false;
     while (element = element.parentNode)
       if (element === ancestor) return true;
     return false;
   }
 
   function descendantOf_contains(element, ancestor) {
     element = $(element), ancestor = $(ancestor);
+    if (!element || !ancestor) return false;
     // Some nodes, like `document`, don't have the "contains" method.
     if (!ancestor.contains) return descendantOf_DOM(element, ancestor);
     return ancestor.contains(element) && ancestor !== element;
   }
 
   function descendantOf_compareDocumentPosition(element, ancestor) {
     element = $(element), ancestor = $(ancestor);
+    if (!element || !ancestor) return false;
     return (element.compareDocumentPosition(ancestor) & 8) === 8;
   }
 

test/unit/tests/dom.test.js

@@ -867,6 +867,9 @@ suite('DOM', function () {
     assert(!$('ancestor').descendantOf($('child')),
      '#ancestor should not be descendant of child');
 
+    assert(!$('child').descendantOf($('non-existent-thing')), 'cannot be a descendant of a non-element');
+    assert(!Element.descendantOf('non-existent-thing', $('ancestor')), 'non-element cannot be a descendant of anything');
+
     assert($('great-grand-child').descendantOf('ancestor'), 'great-grand-child < ancestor');
     assert($('grand-child').descendantOf('ancestor'), 'grand-child < ancestor');
     assert($('great-grand-child').descendantOf('grand-child'), 'great-grand-child < grand-child');