From 777f2be14ef9cc8299537db7491ceb4131ad970e Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Fri, 2 Jan 2015 00:41:33 +1100
Subject: [PATCH] add undefinedToVoid optional transformer

---
 .../transformers/optional-undefined-to-void.js           | 9 +++++++++
 1 file changed, 9 insertions(+)
 create mode 100644 lib/6to5/transformation/transformers/optional-undefined-to-void.js

diff --git a/lib/6to5/transformation/transformers/optional-undefined-to-void.js b/lib/6to5/transformation/transformers/optional-undefined-to-void.js
new file mode 100644
index 0000000000..19875cd90a
--- /dev/null
+++ b/lib/6to5/transformation/transformers/optional-undefined-to-void.js
@@ -0,0 +1,9 @@
+var t = require("../../types");
+
+exports.optional = true;
+
+exports.Identifier = function (node, parent) {
+  if (node.name === "undefined" && t.isReferenced(node, parent)) {
+    return t.unaryExpression("void", t.literal(0), true);
+  }
+};