Major performance boost.

(1) Non-live NodeLists are now implemented using
native Arrays, with an extra `item()` method to
match the NodeList interface.

(2) Using such an array for `Node.childNodes`
is much faster as it doesn't force V8 into
dictionary mode.

(3) The (live) `Node.children` list is now lazily
created, hence the performance penalty is avoided
as long as the property isn't read.

lib/jsdom/level1/core.js

@@ -12,7 +12,7 @@ var core = {
   // Returns Array
   mapDOMNodes : function(parent, recursive, callback) {
     function visit(parent, result) {
-      return parent.childNodes.toArray().reduce(reducer, result);
+      return parent.childNodes.reduce(reducer, result);
     }
 
     function reducer(array, child) {
@@ -139,6 +139,17 @@ core.DOMException.prototype = {
 core.DOMException.prototype.__proto__ = Error.prototype;
 
 core.NodeList = function NodeList(element, query) {
+  if (!query) {
+    // Non-live NodeList
+    var list = element || [];
+    list.item = function(i) {
+      return this[i];
+    };
+    list.toArray = function() {
+      return this;
+    };
+    return list;
+  }
   Object.defineProperties(this, {
     _element: {value: element},
     _query: {value: query},
@@ -150,13 +161,14 @@ core.NodeList = function NodeList(element, query) {
 };
 core.NodeList.prototype = {
   update: function() {
+    var i;
     if (this._element && this._version < this._element._version) {
-      for (var i = 0; i < this._length; i++) {
+      for (i = 0; i < this._length; i++) {
         this[i] = undefined;
       }
       var nodes = this._snapshot = this._query();
       this._length = nodes.length;
-      for (var i = 0; i < nodes.length; i++) {
+      for (i = 0; i < nodes.length; i++) {
         this[i] = nodes[i];
       }
       this._version = this._element._version;
@@ -291,27 +303,17 @@ var attrCopy = function(src, dest, fn) {
 };
 
 core.Node = function Node(ownerDocument) {
-  var self = this;
-
-  this._childNodes = [];
+  this._childNodes = new core.NodeList();
   this._ownerDocument = ownerDocument;
   this._attributes = new core.AttrNodeMap(ownerDocument, this);
-
-  this._childrenList = new core.NodeList(this, function() {
-    return self._childNodes.filter(function(node) {
-      return node.tagName;
-    });
-  });
-
-  this._childNodesList = new core.NodeList(this, function() {
-    return self._childNodes;
-  });
-
+  this._nodeName = null;
+  this._childrenList = null;
   this._version = 0;
   this._nodeValue = null;
   this._parentNode = null;
   this._nodeName = null;
   this._readonly = false;
+  this.style = null;
 };
 
 core.Node.ELEMENT_NODE                = ELEMENT_NODE;
@@ -328,18 +330,6 @@ core.Node.DOCUMENT_FRAGMENT_NODE      = DOCUMENT_FRAGMENT_NODE;
 core.Node.NOTATION_NODE               = NOTATION_NODE;
 
 core.Node.prototype = {
-  _attributes: null,
-  _childNodes: null,
-  _childNodesList: null,
-  _childrenList: null,
-  _version: 0,
-  _nodeValue: null,
-  _parentNode: null,
-  _ownerDocument: null,
-  _attributes: null,
-  _nodeName: null,
-  _readonly: false,
-  style: null,
   ELEMENT_NODE                : ELEMENT_NODE,
   ATTRIBUTE_NODE              : ATTRIBUTE_NODE,
   TEXT_NODE                   : TEXT_NODE,
@@ -354,6 +344,14 @@ core.Node.prototype = {
   NOTATION_NODE               : NOTATION_NODE,
 
   get children() {
+    if (!this._childrenList) {
+      var self = this;
+      this._childrenList = new core.NodeList(this, function() {
+        return self._childNodes.filter(function(node) {
+          return node.tagName;
+        });
+      });
+    }
     return this._childrenList;
   },
   get nodeValue() {
@@ -396,7 +394,7 @@ core.Node.prototype = {
   set lastChild() { throw new core.DOMException();},
 
   get childNodes() {
-    return this._childNodesList;
+    return this._childNodes;
   },
   set childNodes() { throw new core.DOMException();},
 
@@ -520,8 +518,8 @@ core.Node.prototype = {
       this._ownerDocument._version++;
     }
 
-    this._childrenList.update();
-    this._childNodesList.update();
+    if (this._childrenList) this._childrenList.update();
+    //this._childNodesList.update();
   },
 
   _attrModified: function(name, value, oldValue) {
@@ -1508,7 +1506,7 @@ core.Attr.prototype =  {
     for (var i=0,len=this._childNodes.length;i<len;i++) {
       var child = this._childNodes[i];
       if (child.nodeType === ENTITY_REFERENCE_NODE) {
-        val += child.childNodes.toArray().reduce(function(prev, c) {
+        val += child.childNodes.reduce(function(prev, c) {
           return prev += (c.nodeValue || c);
         }, '');
       } else {

lib/jsdom/selectors/index.js

@@ -5,24 +5,19 @@ exports.applyQuerySelectorPrototype = function(dom) {
   };
 
   dom.Document.prototype.querySelectorAll = function(selector) {
-    var self = this;
-    return new dom.NodeList(self, function() {
-      return Sizzle(selector, self);
-    });
+    return new dom.NodeList(Sizzle(selector, this));
   };
 
   dom.Element.prototype.querySelector = function(selector) {
     return Sizzle(selector, this)[0];
   };
 
   dom.Element.prototype.querySelectorAll = function(selector) {
-    var self = this;
-    if( !this.parentNode ){
-      self = this.ownerDocument.createElement("div");
-      self.appendChild(this);
+    var el = this;
+    if (!this.parentNode) {
+      el = this.ownerDocument.createElement("div");
+      el.appendChild(this);
     }
-    return new dom.NodeList(self.ownerDocument, function() {
-      return Sizzle(selector, self.parentNode || self);
-    });
+    return new dom.NodeList(Sizzle(selector, el.parentNode || el));
   };
 };