珠峰架构师成长计划

1. React Hooks #

Hook可以让你在不编写 class组件的情况下使用 state

2. 搭建项目 #

npx create-react-app zhufeng_hooks
cd zhufeng_hooks
yarn start

3. useState #

useState 会返回一对值: 当前状态和一个让你更新它的函数
useState 唯一的参数就是初始 state

const [state, setState] = useState(initialState);

3.1 使用 #

import React from 'react';
import ReactDOM from 'react-dom';
function Counter(){
    const [number,setNumber] = React.useState(0);
    return (
        <>
            <p>{number}</p>
            <button onClick={()=>setNumber(number+1)}>+</button>
        </>
    )
}
function render(){
    ReactDOM.render(<Counter/>,document.getElementById('root'));
}
render();

3.2 实现 #

import React from 'react';
import ReactDOM from 'react-dom';
+let lastState;
+function useState(initialState){
+    lastState = lastState||initialState;
+    function setState(newState){
+        lastState = newState;
+       render();
+    }
+    return [lastState,setState];
+}

function Counter(){
    const [number,setNumber] = useState(0);
    return (
        <>
            <p>{number}</p>
            <button onClick={()=>setNumber(number+1)}>+</button>
        </>
    )
}
function render(){
    ReactDOM.render(<Counter/>,document.getElementById('root'));
}
render();

4. 多useState #

4.1 使用 #

import React from 'react';
import ReactDOM from 'react-dom';
function Counter(){
    const [number1,setNumber1] = React.useState(0);
    const [number2,setNumber2] = React.useState(0);
    return (
        <>
            <p>{number1}</p>
            <button onClick={()=>setNumber1(number1+1)}>+</button>
            <hr/>
            <p>{number2}</p>
            <button onClick={()=>setNumber2(number2+1)}>+</button>
        </>
    )
}
function render(){
    ReactDOM.render(<Counter/>,document.getElementById('root'));
}
render();

4.2 实现 #

import React from 'react';
import ReactDOM from 'react-dom';
let hookStates = [];
let hookIndex = 0;
function useState(initialState){
    //如果有老值取老值,没有取默认值
    hookStates[hookIndex]=hookStates[hookIndex]||initialState;
    //暂存索引
    let currentIndex = hookIndex;
    function setState(newState){
      hookStates[currentIndex]=newState;
      render();
    }
    return [hookStates[hookIndex++],setState];
} 
function Counter(){
    const [number1,setNumber1] = useState(0);
    const [number2,setNumber2] = useState(0);
    return (
        <>
            <p>{number1}</p>
            <button onClick={()=>setNumber1(number1+1)}>+</button>
            <hr/>
            <p>{number2}</p>
            <button onClick={()=>setNumber2(number2+1)}>+</button>
        </>
    )
}
function render(){
    hookIndex =0;
    ReactDOM.render(<Counter/>,document.getElementById('root'));
}
render();

5. 优化 #

我们可以使用useMemo和useCallback来减少渲染

5.1 使用 #

import React from 'react';
import ReactDOM from 'react-dom';
let  Child = ({ onButtonClick, data }) => {
    console.log("Child render");
    return <button onClick={onButtonClick}>{data.number}</button>;
}
Child = React.memo(Child);

function App() {
    const [number, setNumber] = React.useState(0);
    const [name, setName] = React.useState("zhufeng");
    const addClick = React.useCallback(() => setNumber(number + 1), [number]);
    const data = React.useMemo(() => ({ number }), [number]);
    return (
      <div>
        <input value={name} onChange={(e) => setName(e.target.value)} />
        <Child onButtonClick={addClick} data={data} />
      </div>
    );
  }
function render(){
    ReactDOM.render(<App />,document.getElementById('root'));
}
render();

5.2 实现 #

import React from 'react';
import ReactDOM from 'react-dom';
+let hookStates = [];//放着此组件的所有的hooks数据
+let hookIndex = 0;//代表当前的hooks的索引
+function useState(initialState){
+  //如果有老值取老值,没有取默认值
+  hookStates[hookIndex]=hookStates[hookIndex]||initialState;
+  //暂存索引
+  let currentIndex = hookIndex;
+  function setState(newState){
+    hookStates[currentIndex]=newState;
+    render();
+  }
+  return [hookStates[hookIndex++],setState];
+} 
+function useCallback(callback,dependencies){
+  if(hookStates[hookIndex]){
+    let [lastCallback,lastCallbackDeps] = hookStates[hookIndex];
+    let same = dependencies.every((item,index)=>item === lastCallbackDeps[index]);
+    if(same){//如果老依赖和新的依赖都相同,则直接返回老的,如果不一相同,则返回新的
+      hookIndex++;
+      return lastCallback;
+    }else{
+      hookStates[hookIndex++]=[callback,dependencies];
+      return callback;
+    }
+  }else{
+    hookStates[hookIndex++]=[callback,dependencies];
+    return callback;
+  }
+}
+
+function useMemo(factory,dependencies){
+  if(hookStates[hookIndex]){
+    let [memo,lastDeps] = hookStates[hookIndex];
+    let same = dependencies.every((item,index)=>item === lastDeps[index]);
+    if(same){//如果老依赖和新的依赖都相同,则直接返回老的,如果不一相同,则返回新的
+      hookIndex++;
+      return memo;
+    }else{
+      let newMemo = factory();
+      hookStates[hookIndex++]=[newMemo,dependencies];
+      return newMemo;
+    }
+  }else{
+    let newMemo = factory();
+    hookStates[hookIndex++]=[newMemo,dependencies];
+    return newMemo;
+  }
+}


let  Child = ({ onButtonClick, data }) => {
    console.log("Child render");
    return <button onClick={onButtonClick}>{data.number}</button>;
}
Child = React.memo(Child);

function App() {
    const [number, setNumber] = useState(0);
    const [name, setName] = useState("zhufeng");
    const addClick = useCallback(() => setNumber(number + 1), [number]);
    const data = useMemo(() => ({ number }), [number]);
    return (
      <div>
        <input value={name} onChange={(e) => setName(e.target.value)} />
        <Child onButtonClick={addClick} data={data} />
      </div>
    );
}
function render(){
  hookIndex =0;
  ReactDOM.render(<App />,document.getElementById('root'));
}
render();

6. useEffect #

useEffect 就是一个 Effect Hook，给函数组件增加了操作副作用的能力
它跟 class 组件中的 componentDidMount、componentDidUpdate 和 componentWillUnmount 具有相同的用途，只不过被合并成了一个 API

useEffect(didUpdate)

useLayoutEffects

6.1 使用 #

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

function Counter(){
    const [name,setName] = React.useState('珠峰');
    const [number,setNumber] = React.useState(0);
    React.useEffect(() => {
        console.log(number);
     }, [number]);
    return (
        <>
            <p>{name}:{number}</p>
             <button onClick={()=>setName('架构')}>修改名称</button>
            <button onClick={()=>setNumber(number+1)}>+</button>
        </>
    )
}
function render(){
    ReactDOM.render(<Counter/>,document.getElementById('root'));
}
render();

6.2 实现useEffect #

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

+let hookStates = [];
+let hookIndex = 0;
+function useState(initialState){
+  hookStates[hookIndex]=hookStates[hookIndex]||initialState;
+  let currentIndex = hookIndex;
+  function setState(newState){
+    hookStates[currentIndex]=newState;
+    render();
+  }
+  return [hookStates[hookIndex++],setState];
+} 

+function useEffect(callback,dependencies){
+  if(hookStates[hookIndex]){
+      let lastDeps = hookStates[hookIndex];
+      let same = dependencies.every((item,index)=>item === lastDeps[index]);
+      if(same){
+        hookIndex++;
+      }else{
+        hookStates[hookIndex++]=dependencies;
+         setTimeout(callback);
+      }
+  }else{
+     hookStates[hookIndex++]=dependencies;
+      setTimeout(callback);
+  }
+}

function Counter(){
    const [name,setName] = useState('珠峰');
    const [number,setNumber] = useState(0);
    useEffect(() => {
        console.log(number);
     }, [number]);
    return (
        <>
            <p>{name}:{number}</p>
             <button onClick={()=>setName('架构')}>修改名称</button>
            <button onClick={()=>setNumber(number+1)}>+</button>
        </>
    )
}
function render(){
  hookIndex=0;
  ReactDOM.render(<Counter/>,document.getElementById('root'));
}
render();

7. useLayoutEffect #

其函数签名与 useEffect 相同，但它会在所有的 DOM 变更之后同步调用 effect
useEffect不会阻塞浏览器渲染，而 useLayoutEffect 会浏览器渲染
useEffect会在浏览器渲染结束后执行,useLayoutEffect 则是在 DOM 更新完成后,浏览器绘制之前执行

7.1 使用 #

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

const Animate = () => {
  const red = React.useRef();
  const green = React.useRef();
  React.useLayoutEffect(() => {
    red.current.style.transform = `translate(500px)`;
    red.current.style.transition = `all 500ms`;
  });
  React.useEffect(() => {
    green.current.style.transform = `translate(500px)`;
    green.current.style.transition = `all 500ms`;
  });
  let style = { width: '100px', height: '100px' }
  return (
    <div>
      <div style={{ ...style, backgroundColor: 'red' }} ref={red}></div>
      <div style={{ ...style, backgroundColor: 'green' }} ref={green}></div>
    </div>
  )
}
function render() {
  ReactDOM.render(<Animate />, document.getElementById('root'));
}
render();

7.2 实现 #

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

+let hookStates = [];
+let hookIndex = 0;
+function useEffect(callback,dependencies){
+  if(hookStates[hookIndex]){
+      let lastDeps = hookStates[hookIndex];
+      let same = dependencies.every((item,index)=>item === lastDeps[index]);
+      if(same){
+        hookIndex++;
+      }else{
+        hookStates[hookIndex++]=dependencies;
+        setTimeout(callback);
+      }
+  }else{
+     hookStates[hookIndex++]=dependencies;
+     setTimeout(callback);
+  }
+}
+function useLayoutEffect(callback,dependencies){
+  if(hookStates[hookIndex]){
+      let lastDeps = hookStates[hookIndex];
+      let same = dependencies.every((item,index)=>item === lastDeps[index]);
+      if(same){
+        hookIndex++;
+      }else{
+        hookStates[hookIndex++]=dependencies;
+        queueMicrotask(callback);
+      }
+  }else{
+     hookStates[hookIndex++]=dependencies;
+     queueMicrotask(callback);
+  }
+}
const Animate = () => {
  const red = React.useRef();
  const green = React.useRef();
  useLayoutEffect(() => {
    red.current.style.transform = `translate(500px)`;
    red.current.style.transition = `all 500ms`;
  });
  useEffect(() => {
    green.current.style.transform = `translate(500px)`;
    green.current.style.transition = `all 500ms`;
  });
  let style = { width: '100px', height: '100px' }
  return (
    <div>
      <div style={{ ...style, backgroundColor: 'red' }} ref={red}></div>
      <div style={{ ...style, backgroundColor: 'green' }} ref={green}></div>
    </div>
  )
}
function render() {
  ReactDOM.render(<Animate />, document.getElementById('root'));
}
render();

8. useContext #

接收一个 context 对象并返回该 context 的当前值

8.1 使用 #

import React from 'react';
import ReactDOM from 'react-dom';
const CounterContext = React.createContext();
function Counter(){
  let {state,setState} = React.useContext(CounterContext);
  return (
      <>
        <p>{state.number}</p>
        <button onClick={() => setState({number:state.number+1})}>+</button>
        <button onClick={() => setState({number:state.number-1})}>-</button>
      </>
  )
}
function App(){
    const [state, setState] = React.useState({number:0});
    return (
        <CounterContext.Provider value={{state,setState}}>
            <Counter/>
        </CounterContext.Provider>
    )
}
function render(){
    ReactDOM.render(<App/>,document.getElementById('root'));
}
render();

8.2 实现 #

import React from 'react';
import ReactDOM from 'react-dom';
const CounterContext = React.createContext();
+function useContext(context){
+  return context._currentValue;
+}
function Counter(){
  let {state,setState} = useContext(CounterContext);
  return (
      <>
        <p>{state.number}</p>
        <button onClick={() => setState({number:state.number+1})}>+</button>
        <button onClick={() => setState({number:state.number-1})}>-</button>
      </>
  )
}
function App(){
    const [state, setState] = React.useState({number:0});
    return (
        <CounterContext.Provider value={{state,setState}}>
            <Counter/>
        </CounterContext.Provider>
    )
}
function render(){
    ReactDOM.render(<App/>,document.getElementById('root'));
}
render();

9. useReducer #

它接收一个形如 (state, action) => newState 的 reducer，并返回当前的 state 以及与其配套的 dispatch 方法

9.1 使用 #

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

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return state+1;
    case 'decrement':
      return state-1;
    default:
      throw new Error();
  }
}
function Counter(){
    const [state, dispatch] = React.useReducer(reducer, 0);
    return (
        <>
          Count: {state}
          <button onClick={() => dispatch({type: 'increment'})}>+</button>
          <button onClick={() => dispatch({type: 'decrement'})}>-</button>
        </>
    )
}
function render(){
    ReactDOM.render(<Counter/>,document.getElementById('root'));
}
render();

9.2 实现 #

import React from 'react';
import ReactDOM from 'react-dom';
+let hookStates = [];
+let hookIndex = 0;
+function useState(initialState){
+    hookStates[hookIndex]=hookStates[hookIndex]||initialState;
+    let currentIndex = hookIndex;
+    function setState(newState){
+      hookStates[currentIndex]=newState;
+      render();
+    }
+    return [hookStates[hookIndex++],setState];
+} 
+function useReducer(reducer, initialState) {
+  hookStates[hookIndex]=hookStates[hookIndex]||initialState;
+  let currentIndex = hookIndex;
+  function dispatch(action) {
+    hookStates[currentIndex]=reducer(hookStates[currentIndex],action);
+    render();
+  }
+  return [hookStates[hookIndex++], dispatch];
+}
const reducer = (state=0,action)=>{
  switch(action.type){
    case 'add':
      return state+1;
    default:
      return state;
  }
}
function Counter(){
    const [number1,setNumber1] = useState(0);
    const [number2,dispatch] = useReducer(reducer,0);
    return (
        <>
            <p>{number1}</p>
            <button onClick={()=>setNumber1(number1+1)}>+</button>
            <hr/>
            <p>{number2}</p>
            <button onClick={() => dispatch({type: 'add'})}>+</button>
        </>
    )
}
function render(){
    hookIndex=0;
    ReactDOM.render(<Counter/>,document.getElementById('root'));
}
render();