Function flushSync

code/new-context-api/public/app.js:13300–13310

(fn, a)

  // TODO: Batching should be implemented at the renderer level, not within
  // the reconciler.
  function flushSync(fn, a) {
    !!isRendering ? invariant(false, 'flushSync was called from inside a lifecycle method. It cannot be called when React is already rendering.') : void 0;
    var previousIsBatchingUpdates = isBatchingUpdates;
    isBatchingUpdates = true;
    try {
      return syncUpdates(fn, a);
    } finally {
      isBatchingUpdates = previousIsBatchingUpdates;
      performSyncWork();
    }
  }

  function interactiveUpdates(fn, a, b) {
    if (isBatchingInteractiveUpdates) {