Introduce queueMicrotask API

Summary:
Changelog:
[General][Added] - Add global.queueMicrotask

`queueMicrotask` is a relatively recent API defined in the WHATWG HTML spec
and it's been widely adopted by all web browsers and Node.js.

This diff introduced it to React Native by polyfilling it via a lazily-allocated
resolved Promise, or calling directly into a fast path provided by Hermes.

Reviewed By: RSNara

Differential Revision: D29838852

fbshipit-source-id: 8c4378b1b713fb8b0da5e67f92ba2ea9838766f7

Libraries/Core/Timers/queueMicrotask.js

@@ -0,0 +1,41 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @flow
+ */
+
+'use strict';
+
+let resolvedPromise;
+
+/**
+ * Polyfill for the microtask queuening API defined by WHATWG HTMP spec.
+ * https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#dom-queuemicrotask
+ *
+ * The method must queue a microtask to invoke @param {function} callback, and
+ * if the callback throws an exception, report the exception.
+ */
+export default function queueMicrotask(callback: Function) {
+  if (arguments.length < 1) {
+    throw new TypeError(
+      'queueMicrotask must be called with at least one argument (a function to call)',
+    );
+  }
+  if (typeof callback !== 'function') {
+    throw new TypeError('The argument to queueMicrotask must be a function.');
+  }
+
+  // Try to reuse a lazily allocated resolved promise from closure.
+  (resolvedPromise || (resolvedPromise = Promise.resolve()))
+    .then(callback)
+    .catch(error =>
+      // Report the exception until the next tick.
+      setTimeout(() => {
+        throw error;
+      }, 0),
+    );
+}

Libraries/Core/setUpTimers.js

@@ -10,10 +10,21 @@
 
 'use strict';
 
+const {polyfillGlobal} = require('../Utilities/PolyfillFunctions');
+
+if (__DEV__) {
+  if (typeof global.Promise !== 'function') {
+    console.error('Promise should exist before setting up timers.');
+  }
+}
+
+// Currently, Hermes `Promise` is implemented via Internal Bytecode.
+const hasHermesPromiseQueuedToJSVM =
+  global?.HermesInternal?.hasPromise?.() &&
+  global?.HermesInternal?.useEngineQueue?.();
+
 // In bridgeless mode, timers are host functions installed from cpp.
 if (!global.RN$Bridgeless) {
-  const {polyfillGlobal} = require('../Utilities/PolyfillFunctions');
-
   /**
    * Set up timers.
    * You can use this module directly, or just require InitializeCore.
@@ -42,3 +53,18 @@ if (!global.RN$Bridgeless) {
     () => require('./Timers/JSTimers').clearReactNativeMicrotask,
   );
 }
+
+/**
+ * Set up the microtask queueing API, which is required to use the same
+ * microtask queue as the Promise.
+ */
+if (hasHermesPromiseQueuedToJSVM) {
+  // Fast path for Hermes.
+  polyfillGlobal('queueMicrotask', () => global.HermesInternal.enqueueJob);
+} else {
+  // Polyfill it with promise (regardless it's polyfiled or native) otherwise.
+  polyfillGlobal(
+    'queueMicrotask',
+    () => require('./Timers/queueMicrotask.js').default,
+  );
+}