React深入浅出分析Hooks源码

function App() {
const [num, setNum] = useState(0);
const add = () => {
setNum(num + 1);
};
return (
<div>
<p>数字: {num}</p>
<button onClick={add}> +1 </button>
</div>
);
}

function useState(initialValue) {
var value = initialValue
function setState(newVal) {
value = newVal
}
return [value, setState]
}

const MyReact = (function() {
// 定义一个 value 保存在该模块的全局中
let value
return {
useState(initialValue) {
value = value || initialValue
function setState(newVal) {
value = newVal
}
return [value, setState]
}
}
})()

function App() {
const [name, setName] = useState('Kevin');
const [age, setAge] = useState(0);
const handleName = () => {
setNum('Dom');
};
const handleAge = () => {
setAge(age + 1);
};
return (
<div>
<p>姓名: {name}</p>
<button onClick={handleName}> 改名字 </button>
<p>年龄: {age}</p>
<button onClick={handleAge}> 加一岁 </button>
</div>
);
}

const MyReact = (function() {
// 开辟一个储存 hooks 的空间
let hooks = [];
// 指针从 0 开始
let currentHook = 0
return {
// 伪代码 解释重新渲染的时候 会初始化 currentHook
render(Component) {
const Comp = Component()
Comp.render()
currentHook = 0 // 重新渲染时候改变 hooks 指针
return Comp
},
useState(initialValue) {
hooks[currentHook] = hooks[currentHook] || initialValue
const setStateHookIndex = currentHook
// 这里我们暂且默认 setState 方式第一个参数不传 函数，直接传状态
const setState = newState => (hooks[setStateHookIndex] = newState)
return [hooks[currentHook++], setState]
}
}
})()

import React, { useState, useEffect } from 'react';
function App() {
const [name, setName] = useState('Kevin');
const [age, setAge] = useState(0);
const handleName = () => {
setName('Don');
};
const handleAge = () => {
setAge(age + 1);
};
useEffect(()=>{
console.log('useEffect_execute')
}, [age])
return (
<div>
<p>姓名: {name}</p>
<button onClick={handleName}> 改名字 </button>
<p>年龄: {age}</p>
<button onClick={handleAge}> 加一岁 </button>
</div>
);
}
export default App;

const MyReact = (function() {
// 开辟一个储存 hooks 的空间
let hooks = [];
// 指针从 0 开始
let currentHook = 0 ；
// 定义个模块全局的 useEffect 依赖
let deps;
return {
// 伪代码 解释重新渲染的时候 会初始化 currentHook
render(Component) {
const Comp = Component()
Comp.render()
currentHook = 0 // 重新渲染时候改变 hooks 指针
return Comp
},
useState(initialValue) {
hooks[currentHook] = hooks[currentHook] || initialValue
const setStateHookIndex = currentHook
// 这里我们暂且默认 setState 方式第一个参数不传 函数，直接传状态
const setState = newState => (hooks[setStateHookIndex] = newState)
return [hooks[currentHook++], setState]
}
useEffect(callback, depArray) {
const hasNoDeps = !depArray
// 如果没有依赖，说明是第一次渲染，或者是没有传入依赖参数，那么就 为 true
// 有依赖 使用 every 遍历依赖的状态是否变化， 变化就会 true
const hasChangedDeps = deps ? !depArray.every((el, i) => el === deps[i]) : true
// 如果没有依赖， 或者依赖改变
if (hasNoDeps || hasChangedDeps) {
// 执行
callback()
// 更新依赖
deps = depArray
}
},
}
})()

import React, { useState, useEffect } from 'react';
function App() {
const [name, setName] = useState('Kevin');
const [age, setAge] = useState(0);
const handleName = () => {
setName('Don');
};
const handleAge = () => {
setAge(age + 1);
};
useEffect(() => {
setInterval(() => {
setAge(age + 1);
console.log(age)
}, 1000);
}, []);
return (
<div>
<p>姓名: {name}</p>
<button onClick={handleName}> 改名字 </button>
<p>年龄: {age}</p>
<button onClick={handleAge}> 加一岁 </button>
</div>
);
}
export default App;

  // 通过监听 age 的变化。来重新执行 useEffect 内的函数
// 因此这里也就需要记录定时器，当卸载的时候我们去清空定时器，防止多个定时器重新触发
useEffect(() => {
const id = setInterval(() => {
setAge(age + 1);
}, 1000);
return () => {
clearInterval(id)
};
}, [age]);

useEffect(() => {
setInterval(() => {
setAge(age => age + 1);
}, 1000);
}, []);

// 以下是伪代码
// 这里用 dva 发送请求来模拟
import React, { useState, useEffect } from 'react';
import { connect } from 'dva';
function App(props) {
const { goods， dispatch, page } = props;
useEffect(() => {
// 页面完成去发情请求
dispatch({
type: '/goods/list',
payload: {page, pageSize:10},
});
// xxxx
}, [props]);
return (
<div>
<p>商品: {goods}</p>
<button>点击切下一页</button>
</div>
);
}
export default connect(({ goods }) => ({
goods,
}))(App);

const Dispatcher={
useReducer: mountReducer,
useState: mountState,
// xxx 省略其他的方法
}

function mountState<S>(
initialState: (() => S) | S,
): [S, Dispatch<BasicStateAction<S>>] {
/*    mountWorkInProgressHook 方法 返回初始化对象    {        memoizedState: null,        baseState: null,         queue: null,        baseUpdate: null,        next: null,      }    */
const hook = mountWorkInProgressHook();
// 如果传入的是函数 直接执行，所以第一次这个参数是 undefined
if (typeof initialState === 'function') {
initialState = initialState();
}
hook.memoizedState = hook.baseState = initialState;
const queue = (hook.queue = {
last: null,
dispatch: null,
lastRenderedReducer: basicStateReducer,
lastRenderedState: (initialState: any),
});
/*    定义 dispatch 相当于    const dispatch = queue.dispatch =    dispatchAction.bind(null,currentlyRenderingFiber，queue);    */
const dispatch: Dispatch<
BasicStateAction<S>,
> = (queue.dispatch = (dispatchAction.bind(
null,
// Flow doesn't know this is non-null, but we do.
((currentlyRenderingFiber: any): Fiber),
queue,
): any));
// 可以看到这个dispatch就是dispatchAction绑定了对应的 currentlyRenderingFiber 和 queue。最后return：
return [hook.memoizedState, dispatch];
}

function dispatchAction<A>(fiber: Fiber, queue: UpdateQueue<A>, action: A) {
//... 省略验证的代码
const alternate = fiber.alternate;
/*    这其实就是判断这个更新是否是在渲染过程中产生的，currentlyRenderingFiber只有在FunctionalComponent更新的过程中才会被设置，在离开更新的时候设置为null，所以只要存在并更产生更新的Fiber相等，说明这个更新是在当前渲染中产生的，则这是一次reRender。所有更新过程中产生的更新记录在renderPhaseUpdates这个Map上，以每个Hook的queue为key。对于不是更新过程中产生的更新，则直接在queue上执行操作就行了，注意在最后会发起一次scheduleWork的调度。    */
if (
fiber === currentlyRenderingFiber ||
(alternate !== null && alternate === currentlyRenderingFiber)
) {
didScheduleRenderPhaseUpdate = true;
const update: Update<A> = {
expirationTime: renderExpirationTime,
action,
next: null,
};
if (renderPhaseUpdates === null) {
renderPhaseUpdates = new Map();
}
const firstRenderPhaseUpdate = renderPhaseUpdates.get(queue);
if (firstRenderPhaseUpdate === undefined) {
renderPhaseUpdates.set(queue, update);
} else {
// Append the update to the end of the list.
let lastRenderPhaseUpdate = firstRenderPhaseUpdate;
while (lastRenderPhaseUpdate.next !== null) {
lastRenderPhaseUpdate = lastRenderPhaseUpdate.next;
}
lastRenderPhaseUpdate.next = update;
}
} else {
const currentTime = requestCurrentTime();
const expirationTime = computeExpirationForFiber(currentTime, fiber);
const update: Update<A> = {
expirationTime,
action,
next: null,
};
flushPassiveEffects();
// Append the update to the end of the list.
const last = queue.last;
if (last === null) {
// This is the first update. Create a circular list.
update.next = update;
} else {
const first = last.next;
if (first !== null) {
// Still circular.
update.next = first;
}
last.next = update;
}
queue.last = update;
scheduleWork(fiber, expirationTime);
}
}

function mountReducer<S, I, A>(
reducer: (S, A) => S,
initialArg: I,
init?: I => S,
): [S, Dispatch<A>] {
const hook = mountWorkInProgressHook();
let initialState;
if (init !== undefined) {
initialState = init(initialArg);
} else {
initialState = ((initialArg: any): S);
}
// 其他和 useState 一样
hook.memoizedState = hook.baseState = initialState;
const queue = (hook.queue = {
last: null,
dispatch: null,
lastRenderedReducer: reducer,
lastRenderedState: (initialState: any),
});
const dispatch: Dispatch<A> = (queue.dispatch = (dispatchAction.bind(
null,
// Flow doesn't know this is non-null, but we do.
((currentlyRenderingFiber: any): Fiber),
queue,
): any));
return [hook.memoizedState, dispatch];
}

export function useState(initialState) {
return useReducer(invokeOrReturn, initialState);
}

// 模块全局定义
/** @type {number} */
let currentIndex; // 状态的索引，也就是前面模拟实现 useState 时候所说的指针
let currentComponent; // 当前的组件
export function useReducer(reducer, initialState, init) {
/** @type {import('./internal').ReducerHookState} */
// 通过 getHookState 方法来获取 hooks
const hookState = getHookState(currentIndex++);
// 如果没有组件 也就是初始渲染
if (!hookState._component) {
hookState._component = currentComponent;
hookState._value = [
// 没有 init 执行 invokeOrReturn
// invokeOrReturn 方法判断 initialState 是否是函数
// 是函数 initialState(null) 因为初始化没有值默认为null
// 不是函数 直接返回 initialState
!init ? invokeOrReturn(null, initialState) : init(initialState),
action => {
// reducer == invokeOrReturn
const nextValue = reducer(hookState._value[0], action);
// 如果当前的值,不等于 下一个值
// 也就是更新的状态的值,不等于之前的状态的值
if (hookState._value[0]!==nextValue) {
// 储存最新的状态
hookState._value[0] = nextValue;
// 渲染组件
hookState._component.setState({});
}
}
];
}
// hookState._value 数据格式也就是 [satea：any, action:Function] 的数据格式拉
return hookState._value;
}

function getHookState(index) {
if (options._hook) options._hook(currentComponent);
const hooks = currentComponent.__hooks || (currentComponent.__hooks = { _list: [], _pendingEffects: [], _pendingLayoutEffects: [] });
if (index >= hooks._list.length) {
hooks._list.push({});
}
return hooks._list[index];
}

function invokeOrReturn(arg, f) {
return typeof f === 'function' ? f(arg) : f;
}