手写reacthooks的useState

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前言

关于react hooks的useState,在写hooks的时候经常用到,我在之前也有文章写过reactHooks中useState的使用小结 关于useState这个hooks,我们如何手写实现呢?

useState使用小结

1、接收任意类型的入参数,可以是数组、对象、函数等。

2、可以被多次调用,每调用一次都可以解构出不同的状态变量。

3、setState 也可以传入回调函数。改回调函数会被自动传入当前对应的状态变量。

4、被结构出来的状态变量和更改状态变量的方法是1对1绑定的。

5、调用setState后,要重新render函数组件

使用useState的案例

import React, { useState } from "react";

export default function App() {
  // 声明一个新的叫做 “count” 的 state 变量
  const [count, setCount] = useState([0]);
  const [name, setName] = useState("haorooms");
  const [haorooms, setHaorooms] = useState(() => "欢迎haorooms");
  return (
    <div>
      <p>
        You clicked {count}
        {count[0]} times
      </p>
      <p>Call me {name}</p>
      <p>{name} is haorooms blog ?</p>
      <p>{haorooms} is good blog ?</p>
      <button
        onClick={() => {
          setCount([count[0] + 1]);
          setName("haorooms博客");
          setHaorooms((preRooms) => `欢迎${preRooms}`);
        }}
      >
        点击
      </button>
    </div>
  );
}

手写react hooks的useState

import ReactDOM from "react-dom";

let state = [];
let setters = [];
let stateIndex = 0;

const getStateByFn = (v, params) => {
  if (typeof v === "function") {
    const _newState = v(params);
    if (!_newState) throw "You must be return state";
    return _newState;
  }
  return v;
};

function createSetter(index) {
  return function (newState) {
    state[index] = getStateByFn(newState, state[index]);
    render();
  };
}

function useState(initialState) {
  state[stateIndex] = state[stateIndex]
    ? getStateByFn(state[stateIndex])
    : getStateByFn(initialState);
  setters.push(createSetter(stateIndex));
  let value = state[stateIndex];
  let setter = setters[stateIndex];
  stateIndex++;
  return [value, setter];
}

function render() {
  stateIndex = 0;
  ReactDOM.render(<App />, document.getElementById("root"));
}
export default function App() {
      // 声明一个新的叫做 “count” 的 state 变量
      const [count, setCount] = useState([0]);
      const [name, setName] = useState("haorooms");
      const [haorooms, setHaorooms] = useState(() => "欢迎haorooms");
      return (
        <div>
          <p>
            You clicked {count}
            {count[0]} times
          </p>
          <p>Call me {name}</p>
          <p>{name} is haorooms blog ?</p>
          <p>{haorooms} is good blog ?</p>
          <button
            onClick={() => {
              setCount([count[0] + 1]);
              setName("haorooms博客");
              setHaorooms((preRooms) => `欢迎${preRooms}`);
            }}
          >
            点击
          </button>
        </div>
      );
    }

上面代码直接copy出来,作为app.js 直接引入既可以测试了!

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