Fallback to setting __proto__.

Author: ghengeveld

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() {