From a7e8a0945533bd5bc062f4a893757822b3056fa9 Mon Sep 17 00:00:00 2001
From: Ivan Goncharov <ivan.goncharov.ua@gmail.com>
Date: Thu, 1 Apr 2021 14:11:59 +0300
Subject: [PATCH] mapAsyncIterator: make add default value for
 'mapAsyncIterator'

---
 src/subscription/mapAsyncIterator.js | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/subscription/mapAsyncIterator.js b/src/subscription/mapAsyncIterator.js
index 75c8ff5a85..eef86d9ab2 100644
--- a/src/subscription/mapAsyncIterator.js
+++ b/src/subscription/mapAsyncIterator.js
@@ -7,7 +7,9 @@ import type { PromiseOrValue } from '../jsutils/PromiseOrValue';
 export function mapAsyncIterator<T, U>(
   iterable: AsyncIterable<T> | AsyncGenerator<T, void, void>,
   callback: (T) => PromiseOrValue<U>,
-  rejectCallback?: (any) => PromiseOrValue<U>,
+  rejectCallback: (any) => PromiseOrValue<U> = (error) => {
+    throw error;
+  },
 ): AsyncGenerator<U, void, void> {
   // $FlowFixMe[prop-missing]
   const iteratorMethod = iterable[Symbol.asyncIterator];
@@ -28,12 +30,11 @@ export function mapAsyncIterator<T, U>(
       : asyncMapValue(result.value, callback).then(iteratorResult, abruptClose);
   }
 
-  let mapReject;
-  if (rejectCallback) {
-    // Capture rejectCallback to ensure it cannot be null.
-    const reject = rejectCallback;
-    mapReject = (error: mixed) =>
-      asyncMapValue(error, reject).then(iteratorResult, abruptClose);
+  function mapReject(error: mixed) {
+    return asyncMapValue(error, rejectCallback).then(
+      iteratorResult,
+      abruptClose,
+    );
   }
 
   /* TODO: Flow doesn't support symbols as keys: