From e79586515c5f635650afc32976826e01463dcd1d Mon Sep 17 00:00:00 2001
From: Jeremy Ashkenas <jashkenas@gmail.com>
Date: Tue, 18 Oct 2011 16:07:23 -0400
Subject: [PATCH] Issue #329 -- significant change to _.isEqual semantics.

---
 test/objects.js | 12 ++++++------
 underscore.js   | 41 +++++++++++++++--------------------------
 2 files changed, 21 insertions(+), 32 deletions(-)

diff --git a/test/objects.js b/test/objects.js
index c131d920b..5fc4b6a0a 100644
--- a/test/objects.js
+++ b/test/objects.js
@@ -154,8 +154,8 @@ $(document).ready(function() {
     ok(_.isEqual({}, {}), "Empty object literals are equal");
     ok(_.isEqual([], []), "Empty array literals are equal");
     ok(_.isEqual([{}], [{}]), "Empty nested arrays and objects are equal");
-    ok(_.isEqual({length: 0}, []), "Array-like objects and arrays are equal");
-    ok(_.isEqual([], {length: 0}), "Commutative equality is implemented for array-like objects");
+    ok(!_.isEqual({length: 0}, []), "Array-like objects and arrays are not equal.");
+    ok(!_.isEqual([], {length: 0}), "Commutative equality is implemented for array-like objects");
 
     ok(!_.isEqual({}, []), "Object literals and array literals are not equal");
     ok(!_.isEqual([], {}), "Commutative equality is implemented for objects and arrays");
@@ -174,7 +174,7 @@ $(document).ready(function() {
     b.join = b.pop = b.reverse = b.shift = b.slice = b.splice = b.concat = b.sort = b.unshift = null;
 
     // Array elements and properties.
-    ok(_.isEqual(a, b), "Arrays containing equivalent elements and different non-numeric properties are equal");
+    ok(!_.isEqual(a, b), "Arrays containing equivalent elements and different non-numeric properties are not equal");
     a.push("White Rocks");
     ok(!_.isEqual(a, b), "Arrays of different lengths are not equal");
     a.push("East Boulder");
@@ -183,7 +183,7 @@ $(document).ready(function() {
 
     // Sparse arrays.
     ok(_.isEqual(Array(3), Array(3)), "Sparse arrays of identical lengths are equal");
-    ok(!_.isEqual(Array(3), Array(6)), "Sparse arrays of different lengths are not equal");
+    ok(_.isEqual(Array(3), Array(6)), "Sparse arrays of different lengths are equal when both are empty");
 
     // According to the Microsoft deviations spec, section 2.1.26, JScript 5.x treats `undefined`
     // elements in arrays as elisions. Thus, sparse arrays and dense arrays containing `undefined`
@@ -235,8 +235,8 @@ $(document).ready(function() {
 
     // Instances.
     ok(_.isEqual(new First, new First), "Object instances are equal");
-    ok(_.isEqual(new First, new Second), "Objects with different constructors and identical own properties are equal");
-    ok(_.isEqual({value: 1}, new First), "Object instances and objects sharing equivalent properties are identical");
+    ok(!_.isEqual(new First, new Second), "Objects with different constructors and identical own properties are not equal");
+    ok(!_.isEqual({value: 1}, new First), "Object instances and objects sharing equivalent properties are not identical");
     ok(!_.isEqual({value: 2}, new Second), "The prototype chain of objects should not be examined");
 
     // Circular Arrays.
diff --git a/underscore.js b/underscore.js
index d19e26960..5e9d4f3e2 100644
--- a/underscore.js
+++ b/underscore.js
@@ -673,6 +673,8 @@
     }
     // Ensure that both values are objects.
     if (typeA != 'object') return false;
+    // Objects with different constructors are not equal.
+    if (a.constructor !== b.constructor) return false;
     // Assume equality for cyclic structures. The algorithm for detecting cyclic structures is
     // adapted from ES 5.1 section 15.12.3, abstract operation `JO`.
     var length = stack.length;
@@ -684,34 +686,21 @@
     // Add the first object to the stack of traversed objects.
     stack.push(a);
     var size = 0, result = true;
-    if (a.length === +a.length || b.length === +b.length) {
-      // Compare object lengths to determine if a deep comparison is necessary.
-      size = a.length;
-      result = size == b.length;
-      if (result) {
-        // Deep compare array-like object contents, ignoring non-numeric properties.
-        while (size--) {
-          // Ensure commutative equality for sparse arrays.
-          if (!(result = size in a == size in b && eq(a[size], b[size], stack))) break;
-        }
+    // Deep compare objects.
+    for (var key in a) {
+      if (hasOwnProperty.call(a, key)) {
+        // Count the expected number of properties.
+        size++;
+        // Deep compare each member.
+        if (!(result = hasOwnProperty.call(b, key) && eq(a[key], b[key], stack))) break;
       }
-    } else {
-      // Deep compare objects.
-      for (var key in a) {
-        if (hasOwnProperty.call(a, key)) {
-          // Count the expected number of properties.
-          size++;
-          // Deep compare each member.
-          if (!(result = hasOwnProperty.call(b, key) && eq(a[key], b[key], stack))) break;
-        }
-      }
-      // Ensure that both objects contain the same number of properties.
-      if (result) {
-        for (key in b) {
-          if (hasOwnProperty.call(b, key) && !size--) break;
-        }
-        result = !size;
+    }
+    // Ensure that both objects contain the same number of properties.
+    if (result) {
+      for (key in b) {
+        if (hasOwnProperty.call(b, key) && !size--) break;
       }
+      result = !size;
     }
     // Remove the first object from the stack of traversed objects.
     stack.pop();