Function flushSync

lib/assets/react-source/development/react.js:25608–25629

(fn, a)

	  }
	}
	function flushSync(fn, a) {
	  if ((executionContext & (RenderContext | CommitContext)) !== NoContext) {
	    {
	      {
	        throw Error( "flushSync was called from inside a lifecycle method. It cannot be called when React is already rendering." );
	      }
	    }
	  }

	  var prevExecutionContext = executionContext;
	  executionContext |= BatchedContext;

	  try {
	    return runWithPriority$1(ImmediatePriority, fn.bind(null, a));
	  } finally {
	    executionContext = prevExecutionContext; // Flush the immediate callbacks that were scheduled during this batch.
	    // Note that this will happen even if batchedUpdates is higher up
	    // the stack.

	    flushSyncCallbackQueue();
	  }
	}

	function prepareFreshStack(root, expirationTime) {
	  root.finishedWork = null;