From 346253a0d520e24083ab013d247b986cc9b63db9 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <t-weswig@microsoft.com>
Date: Fri, 13 Nov 2015 11:13:10 -0800
Subject: [PATCH] test, first pass at a fix

---
 src/compiler/checker.ts                       |  4 +++
 .../typeGuards/typeGuardTypeOfUndefined.ts    | 28 +++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 tests/cases/conformance/expressions/typeGuards/typeGuardTypeOfUndefined.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ec91b255ae6..6f5a3e67d0a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -200,6 +200,10 @@ namespace ts {
             "symbol": {
                 type: esSymbolType,
                 flags: TypeFlags.ESSymbol
+            },
+            "undefined": {
+                type: undefinedType,
+                flags: TypeFlags.ContainsUndefinedOrNull
             }
         };
 
diff --git a/tests/cases/conformance/expressions/typeGuards/typeGuardTypeOfUndefined.ts b/tests/cases/conformance/expressions/typeGuards/typeGuardTypeOfUndefined.ts
new file mode 100644
index 00000000000..50612449145
--- /dev/null
+++ b/tests/cases/conformance/expressions/typeGuards/typeGuardTypeOfUndefined.ts
@@ -0,0 +1,28 @@
+// undefined type guard adds no new type information
+function test1(a: any) {
+    if (typeof a !== "undefined") {
+        if (typeof a === "boolean") {
+            a;
+        }
+    }
+}
+
+function test2(a: any) {
+    if (typeof a === "undefined") {
+        if (typeof a === "boolean") {
+            a;
+        }
+    }
+}
+
+function test3(a: any) {
+    if (typeof a === "undefined" || typeof a === "boolean") {
+		a;
+    }
+}
+
+function test4(a: any) {
+    if (typeof a !== "undefined" && typeof a === "boolean") {
+		a;
+    }
+}