powercoder23
diff --git a/‎dist/immutable.js
Lines changed: 27 additions & 10 deletions b/‎dist/immutable.js
Lines changed: 27 additions & 10 deletions
@@ -811,21 +811,34 @@
   }
 
   function hashJSObj(obj) {
-    var hash = weakMap && weakMap.get(obj);
-    if (hash) return hash;
+    var hash;
+    if (usingWeakMap) {
+      hash = weakMap.get(obj);
+      if (hash !== undefined) {
+        return hash;
+      }
+    }
 
     hash = obj[UID_HASH_KEY];
-    if (hash) return hash;
+    if (hash !== undefined) {
+      return hash;
+    }
 
     if (!canDefineProperty) {
       hash = obj.propertyIsEnumerable && obj.propertyIsEnumerable[UID_HASH_KEY];
-      if (hash) return hash;
+      if (hash !== undefined) {
+        return hash;
+      }
 
       hash = getIENodeHash(obj);
-      if (hash) return hash;
+      if (hash !== undefined) {
+        return hash;
+      }
     }
 
-    if (Object.isExtensible && !Object.isExtensible(obj)) {
+    if (!usingWeakMap &&
+        typeof Object.isExtensible === 'function' &&
+        Object.isExtensible(obj) === false) {
       throw new Error('Non-extensible objects are not allowed as keys.');
     }
 
@@ -834,7 +847,7 @@
       objHashUID = 0;
     }
 
-    if (weakMap) {
+    if (usingWeakMap) {
       weakMap.set(obj, hash);
     } else if (canDefineProperty) {
       Object.defineProperty(obj, UID_HASH_KEY, {
@@ -843,7 +856,7 @@
         'writable': false,
         'value': hash
       });
-    } else if (obj.propertyIsEnumerable &&
+    } else if (obj.propertyIsEnumerable !== undefined &&
                obj.propertyIsEnumerable === obj.constructor.prototype.propertyIsEnumerable) {
       // Since we can't define a non-enumerable property on the object
       // we'll hijack one of the less-used non-enumerable properties to
@@ -853,7 +866,7 @@
         return this.constructor.prototype.propertyIsEnumerable.apply(this, arguments);
       };
       obj.propertyIsEnumerable[UID_HASH_KEY] = hash;
-    } else if (obj.nodeType) {
+    } else if (obj.nodeType !== undefined) {
       // At this point we couldn't get the IE `uniqueID` to use as a hash
       // and we couldn't use a non-enumerable property to exploit the
       // dontEnum bug so we simply add the `UID_HASH_KEY` on the node
@@ -890,7 +903,11 @@
   }
 
   // If possible, use a WeakMap.
-  var weakMap = typeof WeakMap === 'function' && new WeakMap();
+  var usingWeakMap = typeof WeakMap === 'function';
+  var weakMap;
+  if (usingWeakMap) {
+    weakMap = new WeakMap();
+  }
 
   var objHashUID = 0;