Hook

Hook是React16.8⼀个新增项，它可以让你在不编写 class 的情况
下使⽤ state 以及其他的 React 特性。
Hooks的特点：

• 使你在⽆需修改组件结构的情况下复⽤状态逻辑
• 可将组件中相互关联的部分拆分成更⼩的函数，复杂组件将变得更容易理解
• 更简洁、更易理解的代码
  

useState、useEffect

javascript">import React, { useState, useEffect } from "react";
function FruitList({ fruits, setFruits }) {
// 点击删除
  const delFruit=(delIndex)=>{
       const tem = [...fruits];
       tem.splice(delIndex, 1);
       setFruits(tem);
  }
  return (
    <div>
      <ul>
        {fruits.map((item, index) => {
          return <li key={index} onClick={()=>delFruit(index)}>{item}</li>;
        })}
      </ul>
    </div>
  );
}
function UseState() {
  const [date, setDate] = useState(new Date());
  const [fruits, setFruits] = useState(["苹果", "香蕉"]);
  const [name, setName] = useState("车厘子");
  useEffect(() => {
    const timer = setInterval(() => {
      setDate(new Date());
    }, 1000);
    //记得清理工作，防⽌引起内存泄露
    return () => clearInterval(timer);
  }, [date]);
  return (
    <div>
      <p>{date.toLocaleTimeString()}</p>
      <input value={name} onChange={(e) => setName(e.target.value)} />
      //添加也就是数组合并
      <button onClick={() => setFruits([...fruits,name])}>添加</button>
      //列表显示
      <FruitList fruits={fruits} setFruits={setFruits} />
    </div>
  );
}

export default UseState;

useReducer、useEffect

useReducer是useState的可选项，常⽤于组件有复杂状态逻辑时，类似于redux中reducer概念。
以上代码可修改为

javascript">import React, { useEffect, useReducer } from "react";
function FruitList({ fruits, setFruits }) {
  const delFruit = (delIndex) => {
    const tem = [...fruits];
    tem.splice(delIndex, 1);
    setFruits(tem);
  };
  return (
    <div>
      <ul>
        {fruits.map((item, index) => {
          return (
            <li key={index} onClick={() => delFruit(index)}>
              {item}
            </li>
          );
        })}
      </ul>
    </div>
  );
}
function fruitsReducer(state, action) {
  switch (action.type) {
    case "init":
    case "replace":
      return action.list;
    default:
      return state;
  }
}

export default function HooksReducer() {
  const [fruits, dispatch] = useReducer(fruitsReducer, []);

  useEffect(() => {
    setTimeout(() => {
      dispatch({ type: "init", list: ["apple", "banana"] });
    }, 1000);
    return () => {};
  }, []);
  return (
    <div>
      HooksReducer
      <FruitList
        fruits={fruits}
        setFruits={(newFruitList) =>
          dispatch({ type: "replace", list: newFruitList })
        }
      />
    </div>
  );
}