From 077564cd794a8526e6c9f48286b54f0acf562d71 Mon Sep 17 00:00:00 2001
From: Gert Hengeveld <info@ghengeveld.nl>
Date: Thu, 10 Oct 2019 14:56:04 +0200
Subject: [PATCH 1/2] Avoid extending Promise.

---
 packages/react-async/src/reducer.js | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/packages/react-async/src/reducer.js b/packages/react-async/src/reducer.js
index 3587bcdf..9ef4457b 100644
--- a/packages/react-async/src/reducer.js
+++ b/packages/react-async/src/reducer.js
@@ -1,25 +1,23 @@
 import { getInitialStatus, getIdleStatus, getStatusProps, statusTypes } from "./status"
 
 // This exists to make sure we don't hold any references to user-provided functions
-class NeverSettle extends Promise {
-  constructor() {
-    super(() => {}, () => {})
-    /* istanbul ignore next */
-    if (Object.setPrototypeOf) {
-      // Not available in IE 10, but can be polyfilled
-      Object.setPrototypeOf(this, NeverSettle.prototype)
-    }
-  }
+function NeverSettle() {}
+/* istanbul ignore next */
+if (Object.setPrototypeOf) {
+  // Not available in IE 10, but can be polyfilled
+  Object.setPrototypeOf(NeverSettle, Promise)
+}
+NeverSettle.prototype = Object.assign(Object.create(Promise.prototype), {
   finally() {
     return this
-  }
+  },
   catch() {
     return this
-  }
+  },
   then() {
     return this
-  }
-}
+  },
+})
 
 export const neverSettle = new NeverSettle()
 

From 463c4b51f45100520337c1b0bec790565cd661ef Mon Sep 17 00:00:00 2001
From: Gert Hengeveld <info@ghengeveld.nl>
Date: Thu, 10 Oct 2019 15:09:02 +0200
Subject: [PATCH 2/2] Fallback to setting __proto__.

---
 packages/react-async/src/reducer.js | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/packages/react-async/src/reducer.js b/packages/react-async/src/reducer.js
index 9ef4457b..c377b486 100644
--- a/packages/react-async/src/reducer.js
+++ b/packages/react-async/src/reducer.js
@@ -1,11 +1,14 @@
 import { getInitialStatus, getIdleStatus, getStatusProps, statusTypes } from "./status"
 
 // This exists to make sure we don't hold any references to user-provided functions
+// The way NeverSettle extends from Promise is complicated, but can't be done differently because Babel doesn't support
+// extending built-in classes. See https://babeljs.io/docs/en/caveats/#classes
 function NeverSettle() {}
 /* istanbul ignore next */
 if (Object.setPrototypeOf) {
-  // Not available in IE 10, but can be polyfilled
   Object.setPrototypeOf(NeverSettle, Promise)
+} else {
+  NeverSettle.__proto__ = Promise
 }
 NeverSettle.prototype = Object.assign(Object.create(Promise.prototype), {
   finally() {