React16源码: React中的HostComponent HostText的源码实现

HostComponent & HostText

1 ）概述

HostComponent 就是我们dom原生的这些节点, 如: div, span, p 标签这种
- 使用的是小写字母开头的这些节点一般都认为它是一个 HostComponent
HostText，它是单纯的文本节点
主要关注它们的一个更新过程

2 ）源码

定位到 packages/react-reconciler/src/ReactFiberBeginWork.js
进入 updateHostComponent 这个API

function updateHostComponent(current, workInProgress, renderExpirationTime) {// 这个先跳过pushHostContext(workInProgress);if (current === null) {// 对于整个应用来讲，如果需要复用服务端渲染返回的dom内容，只有 HostComponent 和 HostText// 是需要被复用的，对于 class component 和 function component 本身是不对应于dom的某个节点的// 不会调用 hydrate 相关的东西tryToClaimNextHydratableInstance(workInProgress);}// 获取type和props, 对于 HostComponent 没有 state的概念const type = workInProgress.type;const nextProps = workInProgress.pendingProps;const prevProps = current !== null ? current.memoizedProps : null;let nextChildren = nextProps.children;const isDirectTextChild = shouldSetTextContent(type, nextProps); // 获取该节点是否是 纯字符串if (isDirectTextChild) {// We special case a direct text child of a host node. This is a common// case. We won't handle it as a reified child. We will instead handle// this in the host environment that also have access to this prop. That// avoids allocating another HostText fiber and traversing it.nextChildren = null;} else if (prevProps !== null && shouldSetTextContent(type, prevProps)) {// If we're switching from a direct text child to a normal child, or to// empty, we need to schedule the text content to be reset.// 之前props存在，并且也是文本，则重新设置 tagworkInProgress.effectTag |= ContentReset;}// 在 class component 和 host component 都有这个// 在 class component 是有 instance// 在 dom 节点，也有 instance// 对应这两种节点才能拿到 ref, 否则没有引用markRef(current, workInProgress);// Check the host config to see if the children are offscreen/hidden.// 符合 下面这种情况，其中 当前的更新的优先级不为 Never, workInProgress.mode 要符合 ConcurrentMode 并且 设置了 hidden// 比如模拟自定义的滑动，浏览器的滚动条，通过这个属性来进行一个优化，把不需要显示的组件设置为 hidden// 这样每次滑动，就不需要更新这个组件，减少损耗性能if (renderExpirationTime !== Never &&workInProgress.mode & ConcurrentMode &&shouldDeprioritizeSubtree(type, nextProps)) {// Schedule this fiber to re-render at offscreen priority. Then bailout.workInProgress.expirationTime = Never; // 设置成 Never 这个节点将永不会更新到return null;}// 调用来创建，调和子节点reconcileChildren(current,workInProgress,nextChildren,renderExpirationTime,);return workInProgress.child;
}

进入 shouldSetTextContent
- 来自于 packages/react-reconciler/src/ReactFiberHostConfig.js 这里打包对应的是
  - 这里根据不同平台指向不同的js
- packages/react-reconciler/src/forks/ReactFiberHostConfig.dom.js 看到
```
export * from 'react-dom/src/client/ReactDOMHostConfig';
```
- 定位到 react-dom/src/client/ReactDOMHostConfig.js 中
```
export function shouldSetTextContent(type: string, props: Props): boolean {return (type === 'textarea' ||type === 'option' ||type === 'noscript' ||typeof props.children === 'string' ||typeof props.children === 'number' ||(typeof props.dangerouslySetInnerHTML === 'object' &&props.dangerouslySetInnerHTML !== null &&props.dangerouslySetInnerHTML.__html != null));
}
```
  - 基于此来确定是否继续调和子节点
  - 因为, textarea, option, noscript 这种内部只能显示字符串，里面放新节点没有任何意义
  - string和number是在一个dom节点内的内容
  - 如果有 dangerouslySetInnerHTML 相关也是一个特殊情况

进入 shouldDeprioritizeSubtree

// packages/react-dom/src/client/ReactDOMHostConfig.js
export function shouldDeprioritizeSubtree(type: string, props: Props): boolean {return !!props.hidden;
}

定位到 packages/react-reconciler/src/ReactFiberBeginWork.js#L733
进入 updateHostText 这个API

function updateHostText(current, workInProgress) {// 跳过 hydrate 过程if (current === null) {tryToClaimNextHydratableInstance(workInProgress);}// Nothing to do here. This is terminal. We'll do the completion step// immediately after.return null;
}