From dffd3449a03a4706938e1b037f5828787998ea12 Mon Sep 17 00:00:00 2001
From: Paul Taylor <178183+trxcllnt@users.noreply.github.com>
Date: Fri, 17 May 2024 20:40:28 -0700
Subject: [PATCH] fix(flatmap): flatMap shouldn't throw when the input size is
 smaller than concurrent (#367)

fix #366
---
 spec/asynciterable-operators/flatmap-spec.ts | 7 +++++++
 src/util/returniterator.ts                   | 4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/spec/asynciterable-operators/flatmap-spec.ts b/spec/asynciterable-operators/flatmap-spec.ts
index e3fccb02..c5890530 100644
--- a/spec/asynciterable-operators/flatmap-spec.ts
+++ b/spec/asynciterable-operators/flatmap-spec.ts
@@ -9,6 +9,13 @@ test('AsyncIterable#flatMap with range', async () => {
   expect(await toArray(ys)).toEqual([0, 0, 0, 1, 1, 2]);
 });
 
+test(`AsyncIterable#flatMap with fewer inputs than max concurrent doesn't throw`, async () => {
+  const xs = of(1, 2);
+  const ys = xs.pipe(flatMap(async (x) => range(0, x), 3));
+
+  expect(await toArray(ys)).toEqual([0, 0, 1]);
+});
+
 test('AsyncIterable#flatMap selector returns throw', async () => {
   const err = new Error();
   const xs = of(1, 2, 3);
diff --git a/src/util/returniterator.ts b/src/util/returniterator.ts
index 8e1836ad..6f34b9a5 100644
--- a/src/util/returniterator.ts
+++ b/src/util/returniterator.ts
@@ -2,7 +2,7 @@
  * @ignore
  */
 export function returnIterator<T>(it: Iterator<T>) {
-  if (typeof it.return === 'function') {
+  if (typeof it?.return === 'function') {
     it.return();
   }
 }
@@ -11,7 +11,7 @@ export function returnIterator<T>(it: Iterator<T>) {
  * @ignore
  */
 export async function returnAsyncIterator<T>(it: AsyncIterator<T>): Promise<void> {
-  if (typeof it.return === 'function') {
+  if (typeof it?.return === 'function') {
     await it.return();
   }
 }