kReactRedux.js: 引入useContext,导出Provider函数，实际是用context.Provider包裹的，传入store
导出connect函数：获取store
getMoreProps: 返回一个带state的值和带type的dispatch方法的对象
bindActionCreators: 生成一个actionType:dispatch函数的对象
bindActionCreator：dispatch方法包裹一层

src/pages/MyReactReduxPage.js

import React, { Component } from "react";
import { connect } from "../kReactRedux";

class MyReactReduxPage extends Component {
  render() {
    console.log("props", this.props);
    const { counter, add, minus } = this.props;
    return (
      <div>
        <h1>MyReactReduxPage</h1>
        <p>{counter}</p>
        <button onClick={add}>add</button>
        <button onClick={minus}>minus</button>
      </div>
    );
  }
}

export default connect(
  //mapStateToProps
  state => ({ counter: state }),
  //mapDispatchToProps
  {
    add: () => ({ type: "add" }),
    minus: () => ({ type: "minus" }),
  },
)(MyReactReduxPage);

index.js

import React from "react";
import ReactDOM from "react-dom";
import "./index.css";
import App from "./App";
import store from "./store/MyReactReduxStore";
import { Provider } from "./kReactRedux";

// import store from "./store/ReduxStore";
// import store from "./store/ReactReduxStore";
// import { Provider } from "react-redux";

// const render = () => {
//   ReactDOM.render(<App />, document.getElementById("root"));
// };

// render();

// store.subscribe(render);

ReactDOM.render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById("root"),
);

// ReactDOM.render(<App />, document.getElementById("root"));

kReactRedux.js

import React, { useState, useContext, useEffect } from "react";
// import { bindActionCreators } from "redux";

const Context = React.createContext();

export function Provider({ store, children }) {
  return <Context.Provider value={store}>{children}</Context.Provider>;
}

export const connect = (
  mapStateToProps = state => state,
  mapDispatchToProps = {},
) => Cmp => props => {
  const store = useContext(Context);
  
  const getMoreProps = () => {
    //state => ({ counter: state }),
    const stateProps = mapStateToProps(store.getState());
    const dispatchProps = bindActionCreators(
      mapDispatchToProps,
      store.dispatch,
    );
    return {
      ...stateProps,
      ...dispatchProps,
    };
  };
  
  useEffect(() => {
    store.subscribe(() => {
      setMoreProps({ ...moreProps, ...getMoreProps() });
    });
  }, []);
  const [moreProps, setMoreProps] = useState(getMoreProps());
  console.log(moreProps);
  
  return <Cmp {...props} {...moreProps} />;
};

function bindActionCreator(creator, dispatch) {
//dispatch((creator, dispatch) => ({ type: "add" }))
  return (...args) => dispatch(creator(...args));
}
//{add: ()=>({type:'add'}), minus: ()=>({type: 'minus})
function bindActionCreators(actionCreators, dispatch) {
//actionCreators   {
//     add: () => ({ type: "add" }),
//     minus: () => ({ type: "minus" }),
//   }
  let obj = {};
  //{add:dispatch方法}
  for (let key in actionCreators) {
    obj[key] = bindActionCreator(actionCreators[key], dispatch);
    // console.log(actionCreators[key]);
    
  }
  return obj;
}

src/store/MyReactReduxStore.js

import { createStore } from "redux";

import { counterReducer } from "./counterReducer";

const store = createStore(counterReducer);

export default store;

src/store/counterReducer.js

export function counterReducer(state = 0, action) {
  switch (action.type) {
    case "add":
      return state + 1;
    case "minus":
      return state - 1;
    default:
      return state;
  }
}