From 6b9fc81b642df27d43327e1cc606867ba5cddab4 Mon Sep 17 00:00:00 2001
From: Ben Newman <bn@cs.stanford.edu>
Date: Mon, 23 Sep 2013 11:19:46 -0400
Subject: [PATCH 1/2] Space optimizations for ReactMount.findComponentRoot.

---
 src/core/ReactMount.js | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/core/ReactMount.js b/src/core/ReactMount.js
index 5d636a0a95e..3dff445bc5d 100644
--- a/src/core/ReactMount.js
+++ b/src/core/ReactMount.js
@@ -46,6 +46,9 @@ if (__DEV__) {
   var rootElementsByReactRootID = {};
 }
 
+/** Used to store breadth-first search state in findComponentRoot. */
+var reusableArray = [];
+
 /**
  * @param {DOMElement} container DOM element that may contain a React component.
  * @return {?string} A "reactRoot" ID, if a React component is rendered.
@@ -538,15 +541,19 @@ var ReactMount = {
    * @internal
    */
   findComponentRoot: function(ancestorNode, id) {
-    var firstChildren = [ancestorNode.firstChild];
+    var firstChildren = reusableArray;
     var childIndex = 0;
 
+    firstChildren.length = 0;
+    firstChildren.push(ancestorNode.firstChild);
+
     while (childIndex < firstChildren.length) {
       var child = firstChildren[childIndex++];
       while (child) {
         var childID = ReactMount.getID(child);
         if (childID) {
           if (id === childID) {
+            firstChildren.length = 0;
             return child;
           } else if (ReactInstanceHandles.isAncestorIDOf(childID, id)) {
             // If we find a child whose ID is an ancestor of the given ID,
@@ -556,11 +563,6 @@ var ReactMount = {
             firstChildren.length = childIndex = 0;
             firstChildren.push(child.firstChild);
             break;
-          } else {
-            // TODO This should not be necessary if the ID hierarchy is
-            // correct, but is occasionally necessary if the DOM has been
-            // modified in unexpected ways.
-            firstChildren.push(child.firstChild);
           }
         } else {
           // If this child had no ID, then there's a chance that it was
@@ -574,6 +576,8 @@ var ReactMount = {
       }
     }
 
+    firstChildren.length = 0;
+
     if (__DEV__) {
       console.error(
         'Error while invoking `findComponentRoot` with the following ' +

From 87db648f3e1c0a7edfc5809ff0803f981264d7ae Mon Sep 17 00:00:00 2001
From: Ben Newman <bn@cs.stanford.edu>
Date: Tue, 24 Sep 2013 16:07:37 -0400
Subject: [PATCH 2/2] Address pull request feedback.

---
 src/core/ReactMount.js | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/core/ReactMount.js b/src/core/ReactMount.js
index 3dff445bc5d..a3b0440a1cf 100644
--- a/src/core/ReactMount.js
+++ b/src/core/ReactMount.js
@@ -46,8 +46,8 @@ if (__DEV__) {
   var rootElementsByReactRootID = {};
 }
 
-/** Used to store breadth-first search state in findComponentRoot. */
-var reusableArray = [];
+// Used to store breadth-first search state in findComponentRoot.
+var findComponentRootReusableArray = [];
 
 /**
  * @param {DOMElement} container DOM element that may contain a React component.
@@ -541,11 +541,11 @@ var ReactMount = {
    * @internal
    */
   findComponentRoot: function(ancestorNode, id) {
-    var firstChildren = reusableArray;
+    var firstChildren = findComponentRootReusableArray;
     var childIndex = 0;
 
-    firstChildren.length = 0;
-    firstChildren.push(ancestorNode.firstChild);
+    firstChildren[0] = ancestorNode.firstChild;
+    firstChildren.length = 1;
 
     while (childIndex < firstChildren.length) {
       var child = firstChildren[childIndex++];
@@ -553,17 +553,27 @@ var ReactMount = {
         var childID = ReactMount.getID(child);
         if (childID) {
           if (id === childID) {
+            // Emptying firstChildren/findComponentRootReusableArray is
+            // not necessary for correctness, but it helps the GC reclaim
+            // any nodes that were left at the end of the search.
             firstChildren.length = 0;
+
             return child;
-          } else if (ReactInstanceHandles.isAncestorIDOf(childID, id)) {
+          }
+
+          if (ReactInstanceHandles.isAncestorIDOf(childID, id)) {
             // If we find a child whose ID is an ancestor of the given ID,
             // then we can be sure that we only want to search the subtree
             // rooted at this child, so we can throw out the rest of the
             // search state.
             firstChildren.length = childIndex = 0;
             firstChildren.push(child.firstChild);
+
+            // Ignore the rest of this child's siblings and immediately
+            // continue the outer loop with child.firstChild as child.
             break;
           }
+
         } else {
           // If this child had no ID, then there's a chance that it was
           // injected automatically by the browser, as when a `<table>`
@@ -572,6 +582,7 @@ var ReactMount = {
           // branch, but not before examining the other siblings.
           firstChildren.push(child.firstChild);
         }
+
         child = child.nextSibling;
       }
     }