js react源码中seal和freeze的使用

定义与区别

seal: 封闭。只允许操作入参对象原本就可写的属性
freeze: 冻结，不允许操作所有属性，包括原型与原型链

应用

React源码，开发模式下
初次渲染，ref会被赋值为一个具有current的seal对象，而props.children则是一个childArray的冻结对象

freeze usage

  // Children can be more than one argument, and those are transferred onto
  // the newly allocated props object.
  const childrenLength = arguments.length - 2;
  if (childrenLength === 1) {
    props.children = children;
  } else if (childrenLength > 1) {
    const childArray = Array(childrenLength);
    for (let i = 0; i < childrenLength; i++) {
      childArray[i] = arguments[i + 2];
    }
    if (__DEV__) {
      if (Object.freeze) {
        Object.freeze(childArray);
      }
    }
    props.children = childArray;
  }

ref usage

export function useRef<T>(initialValue: T): {current: T} {
  currentlyRenderingFiber = resolveCurrentlyRenderingFiber();
  workInProgressHook = createWorkInProgressHook();
  let ref;
  
  // 初次渲染，直接赋值为{current: initialValue}，并使用seal封闭，并初始化workInProgressHook.memoizedState
  if (workInProgressHook.memoizedState === null) {
    ref = {current: initialValue};
    if (__DEV__) {
      Object.seal(ref);
    }
    workInProgressHook.memoizedState = ref;
  } 
  // 组件更新
  else {
    ref = workInProgressHook.memoizedState;
  }
  return ref;
}