React DOM update priority

一、作用

二、设置当前更新优先级

备注

• ReactDOMSharedInternals 由 ReactDOMSharedInternals 提供

export function setCurrentUpdatePriority(
  newPriority: EventPriority,
  // Closure will consistently not inline this function when it has arity 1
  // however when it has arity 2 even if the second arg is omitted at every
  // callsite it seems to inline it even when the internal length of the function
  // is much longer. I hope this is consistent enough to rely on across builds
  // 当函数的参数数为 1 时，Closure 一定不会内联这个函数。但是当参数数为 2 时，即使在
  // 每个调用点都省略第二个参数，它似乎仍然会内联这个函数。即使函数的内部长度要长得多。
  // 我希望这种行为在各种构建中足够一致，可以依赖
  IntentionallyUnusedArgument?: empty,
): void {
  ReactDOMSharedInternals.p /* currentUpdatePriority */ = newPriority;
}

三、获取当前更新优先级

备注

• ReactDOMSharedInternals 由 ReactDOMSharedInternals 提供

export function getCurrentUpdatePriority(): EventPriority {
  return ReactDOMSharedInternals.p; /* currentUpdatePriority */
}

四、解决更新优先级

备注

• getEventPriority() 由 ReactDOMEventListener#getEventPriority 实现
• ReactDOMSharedInternals 由 ReactDOMSharedInternals 提供
• NoEventPriority 由 ReactEventPriorities#NoEventPriority 提供
• DefaultEventPriority 由 ReactEventPriorities#DefaultEventPriority 提供

export function resolveUpdatePriority(): EventPriority {
  const updatePriority = ReactDOMSharedInternals.p; /* currentUpdatePriority */
  if (updatePriority !== NoEventPriority) {
    return updatePriority;
  }
  const currentEvent = window.event;
  if (currentEvent === undefined) {
    return DefaultEventPriority;
  }
  return getEventPriority(currentEvent.type);
}

五、以优先级运行

export function runWithPriority<T>(priority: EventPriority, fn: () => T): T {
  const previousPriority = getCurrentUpdatePriority();
  try {
    setCurrentUpdatePriority(priority);
    return fn();
  } finally {
    setCurrentUpdatePriority(previousPriority);
  }
}