diff --git a/diff.js b/diff.js
index d67d1c6..afc8539 100644
--- a/diff.js
+++ b/diff.js
@@ -58,6 +58,24 @@ var MIN_TEXT_LENGTH = 100
 //---------------------------------------------------------------------
 // Helpers...
 
+//	getAllKeys(obj)	
+//		-> Set([key, ..])
+//
+// This is different to Object.keys(..) in that it gets both enumerable 
+// and non-enumerable keys as well as keys defined in prototypes...
+var getAllKeys = function(obj){
+	var res = new Set()
+	while(obj.__proto__ || obj === obj.__proto__){
+		Object.getOwnPropertyNames(obj)
+			.forEach(function(n){
+				res.add(n)
+			})
+		obj = obj.__proto__
+	}
+	return res
+}
+
+
 // 	zip(array, array, ...)
 // 		-> [[item, item, ...], ...]
 //