Return early in module update functions

modules/attributes.js

@@ -1,19 +1,23 @@
-var booleanAttrs = ["allowfullscreen", "async", "autofocus", "autoplay", "checked", "compact", "controls", "declare", 
-                "default", "defaultchecked", "defaultmuted", "defaultselected", "defer", "disabled", "draggable", 
-                "enabled", "formnovalidate", "hidden", "indeterminate", "inert", "ismap", "itemscope", "loop", "multiple", 
-                "muted", "nohref", "noresize", "noshade", "novalidate", "nowrap", "open", "pauseonexit", "readonly", 
-                "required", "reversed", "scoped", "seamless", "selected", "sortable", "spellcheck", "translate", 
+var booleanAttrs = ["allowfullscreen", "async", "autofocus", "autoplay", "checked", "compact", "controls", "declare",
+                "default", "defaultchecked", "defaultmuted", "defaultselected", "defer", "disabled", "draggable",
+                "enabled", "formnovalidate", "hidden", "indeterminate", "inert", "ismap", "itemscope", "loop", "multiple",
+                "muted", "nohref", "noresize", "noshade", "novalidate", "nowrap", "open", "pauseonexit", "readonly",
+                "required", "reversed", "scoped", "seamless", "selected", "sortable", "spellcheck", "translate",
                 "truespeed", "typemustmatch", "visible"];
-    
+
 var booleanAttrsDict = {};
 for(var i=0, len = booleanAttrs.length; i < len; i++) {
   booleanAttrsDict[booleanAttrs[i]] = true;
 }
-    
+
 function updateAttrs(oldVnode, vnode) {
   var key, cur, old, elm = vnode.elm,
-      oldAttrs = oldVnode.data.attrs || {}, attrs = vnode.data.attrs || {};
-  
+      oldAttrs = oldVnode.data.attrs, attrs = vnode.data.attrs;
+
+  if (!oldAttrs && !attrs) return;
+  oldAttrs = oldAttrs || {};
+  attrs = attrs || {};
+
   // update modified attributes, add new attributes
   for (key in attrs) {
     cur = attrs[key];

modules/class.js

@@ -1,7 +1,12 @@
 function updateClass(oldVnode, vnode) {
   var cur, name, elm = vnode.elm,
-      oldClass = oldVnode.data.class || {},
-      klass = vnode.data.class || {};
+      oldClass = oldVnode.data.class,
+      klass = vnode.data.class;
+
+  if (!oldClass && !klass) return;
+  oldClass = oldClass || {};
+  klass = klass || {};
+
   for (name in oldClass) {
     if (!klass[name]) {
       elm.classList.remove(name);

modules/dataset.js

@@ -1,9 +1,13 @@
 function updateDataset(oldVnode, vnode) {
   var elm = vnode.elm,
-    oldDataset = oldVnode.data.dataset || {},
-    dataset = vnode.data.dataset || {},
+    oldDataset = oldVnode.data.dataset,
+    dataset = vnode.data.dataset,
     key
 
+  if (!oldDataset && !dataset) return;
+  oldDataset = oldDataset || {};
+  dataset = dataset || {};
+
   for (key in oldDataset) {
     if (!dataset[key]) {
       delete elm.dataset[key];

modules/eventlisteners.js

@@ -13,8 +13,12 @@ function fnInvoker(o) {
 
 function updateEventListeners(oldVnode, vnode) {
   var name, cur, old, elm = vnode.elm,
-      oldOn = oldVnode.data.on || {}, on = vnode.data.on;
-  if (!on) return;
+      oldOn = oldVnode.data.on, on = vnode.data.on;
+
+  if (!on && !oldOn) return;
+  on = on || {};
+  oldOn = oldOn || {};
+
   for (name in on) {
     cur = on[name];
     old = oldOn[name];

modules/props.js

@@ -1,6 +1,11 @@
 function updateProps(oldVnode, vnode) {
   var key, cur, old, elm = vnode.elm,
-      oldProps = oldVnode.data.props || {}, props = vnode.data.props || {};
+      oldProps = oldVnode.data.props, props = vnode.data.props;
+
+  if (!oldProps && !props) return;
+  oldProps = oldProps || {};
+  props = props || {};
+
   for (key in oldProps) {
     if (!props[key]) {
       delete elm[key];

modules/style.js

@@ -7,9 +7,14 @@ function setNextFrame(obj, prop, val) {
 
 function updateStyle(oldVnode, vnode) {
   var cur, name, elm = vnode.elm,
-      oldStyle = oldVnode.data.style || {},
-      style = vnode.data.style || {},
-      oldHasDel = 'delayed' in oldStyle;
+      oldStyle = oldVnode.data.style,
+      style = vnode.data.style;
+
+  if (!oldStyle && !style) return;
+  oldStyle = oldStyle || {};
+  style = style || {};
+  var oldHasDel = 'delayed' in oldStyle;
+
   for (name in oldStyle) {
     if (!style[name]) {
       elm.style[name] = '';