useState原理

转发地址 github.com/brickspert/…

import React from "react";

import ReactDOM from "react-dom";

import { Button } from "antd";

import "./styles.css";


let _state; // 把 state 存储在外面


function useState(initialValue) {

  _state = _state | initialValue; // 如果没有 _state，说明是第一次执行，把 initialValue 复制给它

  function setState(newState) {

  _state = newState;

  render();

 }

 return [_state, setState];

}


function App() {

  const [count, setCount] = useState(0);


  return (

  <div>

  <div>{count}</div>

  <Button

  onClick={() => {

   setCount(count + 1);

  }}

  >

 点击

  </Button>

  </div>

);

}


const rootElement = document.getElementById("root");

function render() {

  ReactDOM.render(<App />, rootElement);

}

render();