From 42e04ecc7a4c7cef44ce42076141c38dacdce6ab Mon Sep 17 00:00:00 2001
From: Michael Ficarra <git@michael.ficarra.me>
Date: Wed, 19 Oct 2011 23:53:00 -0400
Subject: [PATCH] execution time optimisations for `_.isArguments`, stricter
 es3 fallback

---
 underscore.js | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/underscore.js b/underscore.js
index 182070eb3..27b458428 100644
--- a/underscore.js
+++ b/underscore.js
@@ -739,9 +739,16 @@
   };
 
   // Is a given variable an arguments object?
-  _.isArguments = function(obj) {
-    return toString.call(obj) == '[object Arguments]' || !!(obj && hasOwnProperty.call(obj, 'callee'));
-  };
+  _.isArguments = toString.call(arguments) == '[object Arguments]'
+    ? function(obj) {
+      return toString.call(obj) == '[object Arguments]';
+    }
+    : function(obj) {
+      return obj
+        ? hasOwnProperty.call(obj, 'callee')
+          && hasOwnProperty.call(obj, 'length')
+        : false;
+    };
 
   // Is a given value a function?
   _.isFunction = function(obj) {