Adds support for Document/ShadowRoot activeElement.

Author: bicknellr

src/ShadowDOM/wrappers/Document.js

@@ -20,6 +20,7 @@
   var ShadowRoot = scope.wrappers.ShadowRoot;
   var TreeScope = scope.TreeScope;
   var cloneNode = scope.cloneNode;
+  var defineGetter = scope.defineGetter;
   var defineWrapGetter = scope.defineWrapGetter;
   var elementFromPoint = scope.elementFromPoint;
   var forwardMethodsToWrapper = scope.forwardMethodsToWrapper;
@@ -50,6 +51,31 @@
   defineWrapGetter(Document, 'body');
   defineWrapGetter(Document, 'head');
 
+  defineGetter(Document, 'activeElement', function() {
+    var activeElement = wrap(unwrap(this).activeElement);
+
+    // Loop while activeElement is not a shallow child of this document.
+    while (!this.contains(activeElement)) {
+      var lastHost = activeElement;
+      // Iterate until we hit activeElement's containing ShadowRoot (which
+      // isn't this one) or document.
+      while (activeElement.parentNode) {
+        activeElement = activeElement.parentNode;
+      }
+
+      // If we've reached a ShadowRoot, move to its host.
+      if (activeElement.host) {
+        activeElement = activeElement.host;
+      // Otherwise, we've reached a different document - this document is
+      // not an ancestor of the active element.
+      } else {
+        return null;
+      }
+    }
+
+    return activeElement;
+  });
+
   // document cannot be overridden so we override a bunch of its methods
   // directly on the instance.
 

src/ShadowDOM/wrappers/ShadowRoot.js

@@ -21,6 +21,7 @@
   var setInnerHTML = scope.setInnerHTML;
   var unsafeUnwrap = scope.unsafeUnwrap;
   var unwrap = scope.unwrap;
+  var wrap = scope.wrap;
 
   var shadowHostTable = new WeakMap();
   var nextOlderShadowTreeTable = new WeakMap();
@@ -71,6 +72,30 @@
 
     getSelection: function() {
       return document.getSelection();
+    },
+
+    get activeElement() {
+      var activeElement = wrap(unwrap(this).ownerDocument.activeElement);
+
+      // Loop while activeElement is not a shallow child of this ShadowRoot.
+      while (!this.contains(activeElement)) {
+        // Iterate until we hit activeElement's containing ShadowRoot (which
+        // isn't this one) or document.
+        while (activeElement.parentNode) {
+          activeElement = activeElement.parentNode;
+        }
+
+        // If we've reached a ShadowRoot, move to its host.
+        if (activeElement.host) {
+          activeElement = activeElement.host;
+        // Otherwise, we've reached a document - this ShadowRoot is not an
+        // ancestor of the active element.
+        } else {
+          return null;
+        }
+      }
+
+      return activeElement;
     }
   });