From 365eea6aa7570b738850a1652fdd51b13208fef9 Mon Sep 17 00:00:00 2001
From: Kit Goncharov <ksgoncharov@gmail.com>
Date: Wed, 13 Jul 2011 10:48:16 -0600
Subject: [PATCH] `_.isEqual`: Streamline the deep comparison algorithm and
 remove the dependency on `_.keys`.

---
 test/objects.js |  6 ++++++
 underscore.js   | 15 ++++++++++-----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/test/objects.js b/test/objects.js
index c32a13ad7..08206b913 100644
--- a/test/objects.js
+++ b/test/objects.js
@@ -65,6 +65,11 @@ $(document).ready(function() {
   });
 
   test("objects: isEqual", function() {
+    function Foo(){ this.own = 'a'; }
+    function Bar(){ this.own = 'a'; }
+    Foo.prototype.inherited = 1;
+    Bar.prototype.inherited = 2;
+
     var moe   = {name : 'moe', lucky : [13, 27, 34]};
     var clone = {name : 'moe', lucky : [13, 27, 34]};
     ok(moe != clone, 'basic equality between objects is false');
@@ -80,6 +85,7 @@ $(document).ready(function() {
     ok(_.isEqual({isEqual: function () { return true; }}, {}), 'first object implements `isEqual`');
     ok(_.isEqual({}, {isEqual: function () { return true; }}), 'second object implements `isEqual`');
     ok(!_.isEqual({x: 1, y: undefined}, {x: 1, z: 2}), 'objects with the same number of undefined keys are not equal');
+    ok(!_.isEqual(new Foo, new Bar), 'objects with different inherited properties are not equal');
     ok(!_.isEqual(_({x: 1, y: undefined}).chain(), _({x: 1, z: 2}).chain()), 'wrapped objects are not equal');
     equals(_({x: 1, y: 2}).chain().isEqual(_({x: 1, y: 2}).chain()).value(), true, 'wrapped objects are equal');
 
diff --git a/underscore.js b/underscore.js
index 1a68a9784..14d5c01ed 100644
--- a/underscore.js
+++ b/underscore.js
@@ -632,14 +632,19 @@
     // Add the object to the stack of traversed objects.
     stack.push(a);
     // Deep compare the contents.
-    var aKeys = _.keys(a), bKeys = _.keys(b);
+    var size = 0, sizeRight = 0, result = true, key;
+    for (key in a) {
+      // Count the expected number of properties.
+      size++;
+      // Deep compare each member.
+      if (!(result = key in b && eq(a[key], b[key], stack))) break;
+    }
     // Ensure that both objects contain the same number of properties.
-    var result = aKeys.length == bKeys.length;
     if (result) {
-      // Recursively compare properties.
-      for (var key in a) {
-        if (!(result = key in b && eq(a[key], b[key], stack))) break;
+      for (key in b) {
+        if (++sizeRight > size) break;
       }
+      result = size == sizeRight;
     }
     // Remove the object from the stack of traversed objects.
     stack.pop();