So siehts ganz gut aus !

node_modules/es5-ext/object/key-of.js

@@ -0,0 +1,17 @@
+"use strict";
+
+var eq   = require("./eq")
+  , some = require("./some");
+
+module.exports = function (obj, searchValue) {
+	var result;
+	return some(obj, function (value, name) {
+		if (eq(value, searchValue)) {
+			result = name;
+			return true;
+		}
+		return false;
+	})
+		? result
+		: null;
+};