React Fiber结构的创建步骤

const root = document.getElementById('root');
ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  root
);

export function render(
  element: React$Element<any>,
  container: Container,
  callback: ?Function,
) {
  // 删除一些环境代码
  // ...
  return legacyRenderSubtreeIntoContainer(
    null,
    element,
    container,
    false,
    callback,
  );
}

export function render(
  element: React$Element<any>,
  container: Container,
  callback: ?Function,
) {
  // 删除一些环境代码
  // ...
  return legacyRenderSubtreeIntoContainer(
    null,
    element,
    container,
    false,
    callback,
  );
}

  return createLegacyRoot(
    container,
    shouldHydrate
      ? {
        hydrate: true,
      }
      : undefined,
  );

function FiberRootNode(containerInfo, tag, hydrate) {
  this.tag = tag; // 类型
  this.containerInfo = containerInfo; // container
  this.pendingChildren = null; 
  this.current = null;
  this.pingCache = null;
  this.finishedWork = null;
  this.timeoutHandle = noTimeout;
  this.context = null;
  this.pendingContext = null;
  this.hydrate = hydrate;
  this.callbackNode = null;
  this.callbackPriority = NoLanePriority;
  this.eventTimes = createLaneMap(NoLanes);
  this.expirationTimes = createLaneMap(NoTimestamp);

  this.pendingLanes = NoLanes;
  this.suspendedLanes = NoLanes;
  this.pingedLanes = NoLanes;
  this.mutableReadLanes = NoLanes;
  this.finishedLanes = NoLanes;

  this.entangledLanes = NoLanes;
  this.entanglements = createLaneMap(NoLanes);

  // ....


}

export type RootTag = 0 | 1;

  const uninitializedFiber = createHostRootFiber(tag, strictModeLevelOverride);
  root.current = uninitializedFiber;
  uninitializedFiber.stateNode = root;

const createFiber = function(
  tag: WorkTag,
  pendingProps: mixed,
  key: null | string,
  mode: TypeOfMode,
): Fiber {
  // $FlowFixMe: the shapes are exact here but Flow doesn't like constructors
  return new FiberNode(tag, pendingProps, key, mode);
};

function FiberNode(
  tag: WorkTag,
  pendingProps: mixed,
  key: null | string,
  mode: TypeOfMode,
) {
  // Instance
  this.tag = tag;//组件类型
  this.key = key;//key属性
  this.elementType = null;//元素类型，类函数，显示类，div显示div
  this.type = null;//func或者class
  this.stateNode = null;//dom节点

  // Fiber
  this.return = null;//指向父节点
  this.child = null;//指向子节点
  this.sibling = null;//兄弟节点
  this.index = 0;//

  this.ref = null;

  this.pendingProps = pendingProps;//等待中的属性pendingProps
  this.memoizedProps = null; //记忆属性，一般存放props
  this.updateQueue = null;//更新队列
  this.memoizedState = null;// 一般存放state
  this.dependencies = null;

  this.mode = mode;

  // Effects相关
  this.flags = NoFlags;
  this.subtreeFlags = NoFlags;
  this.deletions = null;

  this.lanes = NoLanes;
  this.childLanes = NoLanes;

  this.alternate = null;//指向workInProgress
}

render() {
    const { name, count } = this.state;
    return (
      <div className="App">
          <Button name={name} />
        {
          count
        }
      </div>
    );
  }

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  root
);

unbatchedUpdates(() => {
  // 更新container
  updateContainer(children, fiberRoot, parentComponent, callback);
});