From 22a240fd39b893982cc397ea8b8bcb78eb31158f Mon Sep 17 00:00:00 2001
From: Ben Alpert <balpert@fb.com>
Date: Sat, 24 Oct 2015 12:19:30 -0700
Subject: [PATCH] Avoid lastProps[key] lookup in initial render

This makes both Firefox and IE 15-20% faster in initial render (!!). On my PE benchmark, createElement is now on par with HTML in Firefox and faster in IE11 (before, it was slower).
---
 src/renderers/dom/shared/ReactDOMComponent.js | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/renderers/dom/shared/ReactDOMComponent.js b/src/renderers/dom/shared/ReactDOMComponent.js
index e8833226ed..967573f34b 100644
--- a/src/renderers/dom/shared/ReactDOMComponent.js
+++ b/src/renderers/dom/shared/ReactDOMComponent.js
@@ -665,7 +665,7 @@ ReactDOMComponent.Mixin = {
       DOMPropertyOperations.setAttributeForID(el, this._rootNodeID);
       // Populate node cache
       ReactMount.getID(el);
-      this._updateDOMProperties({}, props, transaction);
+      this._updateDOMProperties(null, props, transaction);
       var lazyTree = DOMLazyTree(el);
       this._createInitialChildren(transaction, props, context, lazyTree);
       mountImage = lazyTree;
@@ -964,9 +964,9 @@ ReactDOMComponent.Mixin = {
     }
     for (propKey in nextProps) {
       var nextProp = nextProps[propKey];
-      var lastProp = propKey === STYLE ?
-        this._previousStyleCopy :
-        lastProps[propKey];
+      var lastProp =
+        propKey === STYLE ? this._previousStyleCopy :
+        lastProps != null ? lastProps[propKey] : undefined;
       if (!nextProps.hasOwnProperty(propKey) ||
           nextProp === lastProp ||
           nextProp == null && lastProp == null) {