From 96909732db7c767f0172e20efb46305c0d535095 Mon Sep 17 00:00:00 2001
From: Mike Gerwitz <mike@mikegerwitz.com>
Date: Wed, 29 Dec 2010 21:13:21 -0500
Subject: [PATCH] Began adding isInstanceOf, starting with prototype chain
 checks

---
 lib/class.js       | 30 ++++++++++++++++++++++++++++++
 test/test-class.js | 18 ++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/lib/class.js b/lib/class.js
index e660c7d..7963020 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -76,6 +76,36 @@ exports.isClassInstance = function( obj )
 };
 
 
+/**
+ * Determines if the class is an instance of the given type
+ *
+ * The given type can be a class, interface, trait or any other type of object.
+ * It may be used in place of the 'instanceof' operator and contains additional
+ * enhancements that the operator is unable to provide due to prototypal
+ * restrictions.
+ *
+ * @param  {Object}  type      expected type
+ * @param  {Object}  instance  instance to check
+ *
+ * @return  {boolean}  true if instance is an instance of type, otherwise false
+ */
+exports.isInstanceOf = function( type, instance )
+{
+    try
+    {
+        // check prototype chain (with throw an error if type is not a
+        // constructor (function)
+        if ( instance instanceof type )
+        {
+            return true;
+        }
+    }
+    catch ( e ) {}
+
+    return false;
+};
+
+
 /**
  * Default class implementation
  *
diff --git a/test/test-class.js b/test/test-class.js
index c7ec50a..6d8c62b 100644
--- a/test/test-class.js
+++ b/test/test-class.js
@@ -91,3 +91,21 @@ if ( Object.isFrozen )
     );
 }
 
+
+//
+// isInstanceOf
+assert.ok(
+    Class.isInstanceOf( Foo, new Foo() ),
+    "Class instance is recognized by Class.isInstanceOf()"
+);
+
+assert.ok(
+    !( Class.isInstanceOf( Foo, Foo ) ),
+    "Class is not an instance of itself when uninstantiated"
+);
+
+assert.ok(
+    !( Class.isInstanceOf( new Foo(), Foo ) ),
+    "Class is not an instance of its instance"
+);
+