Separate initialize, update and destroy functions.

src/js/lib/guid.js

@@ -0,0 +1,16 @@
+/* Copyright (c) 2015 Hyunje Alex Jun and other contributors
+ * Licensed under the MIT License
+ */
+'use strict';
+
+module.exports = (function() {
+  function s4() {
+    return Math.floor((1 + Math.random()) * 0x10000)
+               .toString(16)
+               .substring(1);
+  }
+  return function() {
+    return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
+           s4() + '-' + s4() + s4() + s4();
+  };
+})();