前端面试总结之 React Hooks

class App extends React.Component<any, any> {
    handleClick2;

    constructor(props) {
        super(props);
        this.state = {
            num: 1,
            title: ' react study'
        };
        this.handleClick2 = this.handleClick1.bind(this);
    }

    handleClick1() {
        this.setState({
            num: this.state.num + 1,
        })
    }

    handleClick3 = () => {
        this.setState({
            num: this.state.num + 1,
        })
    };

    render() {
        return (<div>
            <h2>Ann, {this.state.num}</h2>
            <button onClick={this.handleClick2}>btn1</button>
            <button onClick={this.handleClick1.bind(this)}>btn2</button>
            <button onClick={() => this.handleClick1()}>btn3</button>
            <button onClick={this.handleClick3}>btn4</button>
        </div>)
    }
}

function useState(initialState) {
    currentHookNameInDev = 'useState';
    mountHookTypesDev();
    var prevDispatcher = ReactCurrentDispatcher$1.current;
    ReactCurrentDispatcher$1.current = InvalidNestedHooksDispatcherOnMountInDEV;

    try {
        return mountState(initialState);
    } finally {
        ReactCurrentDispatcher$1.current = prevDispatcher;
    }
}
function mountState(initialState) {
    var hook = mountWorkInProgressHook();

    if (typeof initialState === 'function') {
        initialState = initialState();
    }

    hook.memoizedState = hook.baseState = initialState;
    var queue = {
        pending: null,
        interleaved: null,
        lanes: NoLanes,
        dispatch: null,
        lastRenderedReducer: basicStateReducer,
        lastRenderedState: initialState
    };
    hook.queue = queue;
    var dispatch = queue.dispatch = dispatchSetState.bind(null, currentlyRenderingFiber$1, queue);
    return [hook.memoizedState, dispatch];
}
function mountWorkInProgressHook() {
    var hook = {
        memoizedState: null,
        baseState: null,
        baseQueue: null,
        queue: null,
        next: null
    };

    if (workInProgressHook === null) {
        // This is the first hook in the list
        currentlyRenderingFiber$1.memoizedState = workInProgressHook = hook;
    } else {
        // Append to the end of the list
        workInProgressHook = workInProgressHook.next = hook;
    }

    return workInProgressHook;
}

function dispatchSetState(fiber, queue, action) {
  {
    if (typeof arguments[3] === 'function') {
      error("State updates from the useState() and useReducer() Hooks don't support the " + 'second callback argument. To execute a side effect after ' + 'rendering, declare it in the component body with useEffect().');
    }
  }

  var lane = requestUpdateLane(fiber);
  var update = {
    lane: lane,
    action: action,
    hasEagerState: false,
    eagerState: null,
    next: null
  };

  if (isRenderPhaseUpdate(fiber)) {
    enqueueRenderPhaseUpdate(queue, update);
  } else {
    var alternate = fiber.alternate;

    if (fiber.lanes === NoLanes && (alternate === null || alternate.lanes === NoLanes)) {
      // The queue is currently empty, which means we can eagerly compute the
      // next state before entering the render phase. If the new state is the
      // same as the current state, we may be able to bail out entirely.
      var lastRenderedReducer = queue.lastRenderedReducer;

      if (lastRenderedReducer !== null) {
        var prevDispatcher;

        {
          prevDispatcher = ReactCurrentDispatcher$1.current;
          ReactCurrentDispatcher$1.current = InvalidNestedHooksDispatcherOnUpdateInDEV;
        }

        try {
          var currentState = queue.lastRenderedState;
          var eagerState = lastRenderedReducer(currentState, action); // Stash the eagerly computed state, and the reducer used to compute
          // it, on the update object. If the reducer hasn't changed by the
          // time we enter the render phase, then the eager state can be used
          // without calling the reducer again.

          update.hasEagerState = true;
          update.eagerState = eagerState;

          if (objectIs(eagerState, currentState)) {
            // Fast path. We can bail out without scheduling React to re-render.
            // It's still possible that we'll need to rebase this update later,
            // if the component re-renders for a different reason and by that
            // time the reducer has changed.
            // TODO: Do we still need to entangle transitions in this case?
            enqueueConcurrentHookUpdateAndEagerlyBailout(fiber, queue, update, lane);
            return;
          }
        } catch (error) {// Suppress the error. It will throw again in the render phase.
        } finally {
          {
            ReactCurrentDispatcher$1.current = prevDispatcher;
          }
        }
      }
    }

    var root = enqueueConcurrentHookUpdate(fiber, queue, update, lane);

    if (root !== null) {
      var eventTime = requestEventTime();
      scheduleUpdateOnFiber(root, fiber, lane, eventTime);
      entangleTransitionUpdate(root, queue, lane);
    }
  }
  markUpdateInDevTools(fiber, lane);
}

import React from 'react';
import ReactDOM from 'react-dom';

let firstWorkInProgressHook = { memoizedState: null, next: null };
let workInProgressHook;

function useState(initState) {
  let currentHook = workInProgressHook.next ? workInProgressHook.next : { memoizedState: initState, next: null };

  function setState(newState) {
    currentHook.memoizedState = newState;
    render();
  }
  // 这就是为什么 useState 书写顺序很重要的原因
  // 假如某个 useState 没有执行，会导致指针移动出错，数据存取出错
  if (workInProgressHook.next) {
    // 这里只有组件刷新的时候，才会进入
    // 根据书写顺序来取对应的值
    // console.log(workInProgressHook);
    workInProgressHook = workInProgressHook.next;
  } else {
    // 只有在组件初始化加载时，才会进入
    // 根据书写顺序，存储对应的数据
    // 将 firstWorkInProgressHook 变成一个链表结构
    workInProgressHook.next = currentHook;
    // 将 workInProgressHook 指向 {memoizedState: initState, next: null}
    workInProgressHook = currentHook;
    // console.log(firstWorkInProgressHook);
  }
  return [currentHook.memoizedState, setState];
}

function Counter() {
  // 每次组件重新渲染的时候，这里的 useState 都会重新执行
  const [name, setName] = useState('计数器');
  const [number, setNumber] = useState(0);
  return (
    <>
      <p>{name}:{number}</p>
      <button onClick={() => setName('新计数器' + Date.now())}>新计数器</button>
      <button onClick={() => setNumber(number + 1)}>+</button>
    </>
  )
}

export function render() {
  // 每次重新渲染的时候，都将 workInProgressHook 指向 firstWorkInProgressHook
  workInProgressHook = firstWorkInProgressHook;
  ReactDOM.render(<Counter />, document.getElementById('state'));
}