React源码中的queueMacroTask

/**
 * Copyright © Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */
let didWarnAboutMessageChannel = false;
let enqueueTaskImpl = null;
export default function enqueueTask(task: () => void): void {
   if (enqueueTaskImpl === null) {
     try {
       // read require off the module object to get around the bundlers.
       // we don't want them to detect a require and bundle a Node polyfill.
       const requireString = ('require' + Math.random()).slice(0, 7);
       // $FlowFixMe[invalid-computed-prop]
       const nodeRequire = module && module[requireString];
       // assuming we're in node, let's try to get node's
       // version of setImmediate, bypassing fake timers if any.
       enqueueTaskImpl = nodeRequire.call(module, 'timers').setImmediate;
       } catch (_err) {
       // we're in a browser
       // we can't use regular timers because they may still be faked
       // so we try MessageChannel+postMessage instead
       enqueueTaskImpl = function (callback: () => void) {
       if (__DEV__) {
         if (didWarnAboutMessageChannel === false) {
           didWarnAboutMessageChannel = true;
           if (typeof MessageChannel === 'undefined') {
             console.error(
             'This browser does not have a MessageChannel implementation, ' +
             'so enqueuing tasks via await act(async () => …) will fail. ' +
             'Please file an issue at https://github.com/facebook/react/issues ' +
             'if you encounter this warning.',
             );
           }
         }
       }
       const channel = new MessageChannel();
       channel.port1.onmessage = callback;
       channel.port2.postMessage(undefined);
     };
   }
  }
  return enqueueTaskImpl(task);
}