From ed89a3e0f8524754f1f9c8650bda2c9200233f1b Mon Sep 17 00:00:00 2001
From: John-David Dalton <john.david.dalton@gmail.com>
Date: Tue, 24 Jul 2012 01:45:34 -0700
Subject: [PATCH] Check for custom `isEqual` methods in `_.isEqual` before
 other comparisons and add cross-browser support for `arguments` objects.

Former-commit-id: 56e40f670309aeb0dcda7868c8aa84b5909db1f1
---
 lodash.js    | 20 ++++++++++----------
 test/test.js | 14 ++++++++++++++
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/lodash.js b/lodash.js
index 9f05ed000..28cedea08 100644
--- a/lodash.js
+++ b/lodash.js
@@ -2913,29 +2913,29 @@
   function isEqual(a, b, stack) {
     stack || (stack = []);
 
-    // exit early for identical values
-    if (a === b) {
-      // treat `+0` vs. `-0` as not equal
-      return a !== 0 || (1 / a == 1 / b);
-    }
     // a strict comparison is necessary because `null == undefined`
     if (a == null || b == null) {
       return a === b;
     }
-    // unwrap any wrapped objects
+    // unwrap any LoDash wrapped values
     if (a._chain) {
       a = a._wrapped;
     }
     if (b._chain) {
       b = b._wrapped;
     }
-    // invoke a custom `isEqual` method if one is provided
+    // use custom `isEqual` method if available
     if (a.isEqual && toString.call(a.isEqual) == funcClass) {
       return a.isEqual(b);
     }
     if (b.isEqual && toString.call(b.isEqual) == funcClass) {
       return b.isEqual(a);
     }
+    // exit early for identical values
+    if (a === b) {
+      // treat `+0` vs. `-0` as not equal
+      return a !== 0 || (1 / a == 1 / b);
+    }
     // compare [[Class]] names
     var className = toString.call(a);
     if (className != toString.call(b)) {
@@ -2979,12 +2979,12 @@
         result = true,
         size = 0;
 
-    // add the first collection to the stack of traversed objects
+    // add `a` to the stack of traversed objects
     stack.push(a);
 
     // recursively compare objects and arrays (susceptible to call stack limits)
-    if (className == arrayClass) {
-      // compare array lengths to determine if a deep comparison is necessary
+    if (arrayLikeClasses[className] || (noArgsClass && isArguments(value))) {
+      // compare lengths to determine if a deep comparison is necessary
       size = a.length;
       result = size == b.length;
 
diff --git a/test/test.js b/test/test.js
index 0d8d6b6d0..fc40c42dd 100644
--- a/test/test.js
+++ b/test/test.js
@@ -671,6 +671,20 @@
   QUnit.module('lodash.isEqual');
 
   (function() {
+    test('should work with `arguments` objects (test in IE < 9)', function() {
+      var args1 = (function() { return arguments; }(1, 2, 3)),
+          args2 = (function() { return arguments; }(1, 2, 3)),
+          args3 = (function() { return arguments; }(1, 2));
+
+      equal(_.isEqual(args1, args2), true);
+      equal(_.isEqual(args1, args3), false);
+    });
+
+    test('should respect custom `isEqual` result despite objects strict equaling each other', function() {
+      var object = { 'isEqual': function() { return false; } };
+      equal(_.isEqual(object, object), false);
+    });
+
     test('fixes the JScript [[DontEnum]] bug (test in IE < 9)', function() {
       equal(_.isEqual(shadowed, {}), false);
     });