fix(tsc): add .at() types manually to tsc (#11443)

Fixes: #11441

1 files changed, 12 insertions, 0 deletions

diff --git a/cli/tests/unit/esnext_test.ts b/cli/tests/unit/esnext_test.ts
new file mode 100644
index 000000000..558c678bc
--- /dev/null
+++ b/cli/tests/unit/esnext_test.ts
@@ -0,0 +1,12 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+import { assertEquals, unitTest } from "./test_util.ts";
+
+// TODO(@kitsonk) remove when we are no longer patching TypeScript to have
+// these types available.
+
+unitTest(function typeCheckingEsNextArrayString() {
+  const a = "abcdef";
+  assertEquals(a.at(-1), "f");
+  const b = ["a", "b", "c", "d", "e", "f"];
+  assertEquals(b.at(-1), "f");
+});