https://github.com/facebook/react/blob/30b47103d4354d9187dc0f1fb804855a5208ca9f/packages/scheduler/src/Scheduler.js#L180-L185
var priorityLevel;
  switch (currentPriorityLevel) {
    case ImmediatePriority:
    case UserBlockingPriority:
    case NormalPriority:
      
      priorityLevel = NormalPriority;
      break;
    default:
      
      priorityLevel = currentPriorityLevel;
      break;
  }
  var previousPriorityLevel = currentPriorityLevel;
  currentPriorityLevel = priorityLevel;
  try {
    return eventHandler();
  } finally {
    currentPriorityLevel = previousPriorityLevel;
  }
}
function unstable_wrapCallback(callback) {