useReducer 简单实现

import React from "react";
import ReactDOM from "react-dom";
//老状态,动作
function reducer(state, action) {
  if (action.type === "add") {
    return state + 1;
  } else {
    return state;
  }
}
let lastState;
function useReducer(reducer, initialState) {
  lastState = lastState || initialState;
  function dispatch(action) {
    lastState = reducer(lastState, action);
    render();
  }
  return [lastState, dispatch];
}
//useReducer
//{type:'add'}就是action是一个普通对象
function Counter() {
  let [state, dispatch] = useReducer(reducer, 0);
  return (
    <div>
      <p>{state}</p>
      <button onClick={() => dispatch({ type: "add" })}>+</button>
    </div>
  );
}
function render() {
  ReactDOM.render(<Counter />, document.getElementById("root"));
}
render();

转珠峰公开课