From bc709a87adde465c6c2bba450e60cdae4c712de1 Mon Sep 17 00:00:00 2001
From: Andy <anhans@microsoft.com>
Date: Mon, 17 Sep 2018 15:14:09 -0700
Subject: [PATCH] Fix bug where array element is undefined (#26433)

* Fix bug where array element is undefined

* Better fix
---
 src/compiler/checker.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 78628da2749..75349ee8ef6 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -3470,8 +3470,8 @@ namespace ts {
                             const arity = getTypeReferenceArity(type);
                             const tupleConstituentNodes = mapToTypeNodes(typeArguments.slice(0, arity), context);
                             const hasRestElement = (<TupleType>type.target).hasRestElement;
-                            if (tupleConstituentNodes && tupleConstituentNodes.length > 0) {
-                                for (let i = (<TupleType>type.target).minLength; i < arity; i++) {
+                            if (tupleConstituentNodes) {
+                                for (let i = (<TupleType>type.target).minLength; i < Math.min(arity, tupleConstituentNodes.length); i++) {
                                     tupleConstituentNodes[i] = hasRestElement && i === arity - 1 ?
                                         createRestTypeNode(createArrayTypeNode(tupleConstituentNodes[i])) :
                                         createOptionalTypeNode(tupleConstituentNodes[i]);