Immutable.js出自Facebook，是最流行的不可变数据结构的实现之一。它实现了完全的持久化数据结构，使用结构共享。所有的更新操作都会返回新的值，但是在内部结构是共享的，来减少内存占用。Immutablejs官网

在上一篇介绍redux的文章，我们可以看到在创建的reducer中进行数据更改的时候，会使用…来复制状态数据，为的就是不对原数据进行直接修改，只做替换，就是为了实现react的数据不可变immutable。也就是说如果state的数据比较简单那还好，万一比较复杂，就要复制很多这样的结构数据，很占内存影响app的性能。

安装

npm i immutable redux-immutable -S

替换redux中的combineReducers，改用redux-immutable里面的

import { createStore } from "redux";
import { combineReducers } from "redux-immutable";

import { CounterReducer } from "./CounterReducer";

const reducers = combineReducers({
  count: CounterReducer,
});

let store = createStore(reducers);

store.subscribe(() => console.log(store.getState()));

export default store;

改造reducers里面的代码

import { fromJS } from "immutable";
const initialState = fromJS({
  counter: 0,
  userInfo: {
    name: "John Doe",
    age: 25,
  },
});
function CounterReducer(state = initialState, action) {
  switch (action.type) {
    case "ADD":
      return state.update("counter", (val) => {
        console.log("🚀 ~ returnstate.update ~ val:", val);
        return val + 1;
      });
    case "DEC":
      return state.update('counter',value => value - 1)
    default:
      return state;
  }
}

export { CounterReducer };

组件里面使用方式变化
DemoA.js

import store from "../../store";
function DemoA() {
  const count = store.getState().get("count").get("counter");
  return (
    <div>
      <p> Demo A count: {count}</p>
    </div>
  );
}
export default DemoA;

DemoB.js

import store from "../../store";

function DemoB() {
  const data = store.getState().get("count");
  return (
    <div>
      <p>Demo B</p>
      <div>
        <span>name: {data.getIn(["userInfo", "name"])}</span> <br />
        <span>age: {data.getIn(["userInfo", "age"])}</span>
        <span>count:{data.get("counter")}</span>
      </div>
      <button onClick={() => store.dispatch({ type: "ADD" })}>add count</button>
    </div>
  );
}
export default DemoB;

index.js

import DemoA from "./DemoA";
import DemoB from "./DemoB";
import store from "../../store/index";
import { useEffect, useState } from "react";
function Redux() {
  console.log(store.getState(), "store.getState()");
  const [counter, setCount] = useState(
    store.getState().get("count").get("counter")
  );
  useEffect(() => {
    const unsubscribe = store.subscribe(() => {
      console.log("aaaa");
      setCount(store.getState().get("count").get("counter"));
    });
    return () => {
      unsubscribe();
    };
  }, [counter]);
  return (
    <div>
      Redux
      <hr />
      parent count:{counter}
      <DemoA />
      <DemoB />
    </div>
  );
}

export default Redux;

实现了同样的效果