From d38ee1eaf71fb6f92418ba5c2bf53b7b08366a17 Mon Sep 17 00:00:00 2001
From: Arthur Ozga <arozga@microsoft.com>
Date: Wed, 3 May 2017 13:26:24 -0700
Subject: [PATCH] restore `startsWith`

---
 src/compiler/core.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 6de1d62c14e..de560d89d40 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1729,8 +1729,8 @@ namespace ts {
     }
 
     /* @internal */
-    export function startsWith(str: string, prefix: string): boolean {
-        return str.indexOf(prefix) === 0;
+    export function startsWith(str: string, prefix: string | undefined): boolean {
+        return str.lastIndexOf(prefix, 0) === 0;
     }
 
     /* @internal */