美团面试官：那你讲一讲Vuex吧

//index.js
import { createStore } from './gvuex.js'
const store = createStore({
  // 定义store的状态
  state() {
    return {
      count: 1 
    }
  },
  // 定义获取state状态数据的计算属性getters，以下的值都被认为是state的派生值
  getters: {
    double(state) { 
      return state.count * 2
    }
  },
  // 定义修改state状态数据的方法mutations
  mutations: {
    add(state) { 
      state.count++
    }
  },
  // 定义异步操作的方法actions
  actions: {
    asyncAdd({ commit }) { 
      setTimeout(() => {
        commit('add')
      }, 1000)
    }
  }
})

// App.vue
<script setup>
import { useStore } from '../store/gvuex'
import { computed } from 'vue'
let store = useStore();
let count = computed(()=>{ store.state.count })
let double = computed(()=>{ store.getters.double })
function add() {
  store.commit('add')
}
function asyncAdd() {
  store.dispatch('asyncAdd')
}
</script>
<template>
<div class="">
  {{ count }} * 2 = {{ double }}
  <button @click="add">add</button>
  <button @click="asyncAdd">async add</button>
</div>
</template>
<style scoped>
</style>

import { createApp } from 'vue'
import store from './store'
import App from './App.vue'
const app = createApp(App)
app
    .use(store)
    .mount('#app')

import { reactive, inject } from 'vue'
// 定义了一个全局的 key，用于在 Vue 组件中通过 inject API 访问 store 对象
const STORE_KEY = '__store__'
// 用于获取当前组件的 store 对象
function useStore() {
    return inject(STORE_KEY)
}
// Store 类，用于管理应用程序状态
class Store {
    // 构造函数，接收一个包含 state、mutations、actions 和 getters 函数的对象 options，然后将它们保存到实例属性中
    constructor(options) {
        this.$options = options;
        // 使用 Vue.js 的 reactive API 将 state 数据转换为响应式对象，并保存到实例属性 _state 中        
        this._state = reactive({
            data: options.state()
        })
        // 将 mutations 和 actions 函数保存到实例属性中
        this._mutations = options.mutations
        this._actions = options.actions;
        // 初始化 getters 属性为空对象
        this.getters = {};
        // 遍历所有的 getters 函数，将其封装成 computed 属性并保存到实例属性 getters 中
        Object.keys(options.getters).forEach(name => {
            const fn = options.getters(name);
            this.getters[name] = computed(() => fn(this.state));
        })
    }
    // 用于获取当前状态数据
    get state() {
        return this._state.data
    }
    // 获取mutation内定义的函数并执行
    commit = (type, payload) => {
        const entry = this._mutations[type]
        entry && entry(this.state, payload)
    }
    // 获取actions内定义的函数并返回函数执行结果
    // 简略版dispatch
    dispatch = (type, payload) => { 
        const entry = this._actions[type];
        return entry && entry(this, payload)
    }
    // 将当前 store 实例注册到 Vue.js 应用程序中
    install(app) {
        app.provide(STORE_KEY, this)
    }
}
// 创建一个新的 Store 实例并返回
function createStore(options) {
    return new Store(options);
}
// 导出 createStore 和 useStore 函数，用于在 Vue.js 应用程序中管理状态
export {
    createStore,
    useStore
}

Store.prototype.dispatch = function dispatch (_type, _payload) {
    var this$1$1 = this;
  // check object-style dispatch
  var ref = unifyObjectStyle(_type, _payload);
    var type = ref.type;
    var payload = ref.payload;
  var action = { type: type, payload: payload };
  var entry = this._actions[type];
  if (!entry) {
    if ((process.env.NODE_ENV !== 'production')) {
      console.error(("[vuex] unknown action type: " + type));
    }
    return
  }
  try {
    this._actionSubscribers
      .slice() // shallow copy to prevent iterator invalidation if subscriber synchronously calls unsubscribe
      .filter(function (sub) { return sub.before; })
      .forEach(function (sub) { return sub.before(action, this$1$1.state); });
  } catch (e) {
    if ((process.env.NODE_ENV !== 'production')) {
      console.warn("[vuex] error in before action subscribers: ");
      console.error(e);
    }
  }
  var result = entry.length > 1
    ? Promise.all(entry.map(function (handler) { return handler(payload); }))
    : entry[0](payload);
  return new Promise(function (resolve, reject) {
    result.then(function (res) {
      try {
        this$1$1._actionSubscribers
          .filter(function (sub) { return sub.after; })
          .forEach(function (sub) { return sub.after(action, this$1$1.state); });
      } catch (e) {
        if ((process.env.NODE_ENV !== 'production')) {
          console.warn("[vuex] error in after action subscribers: ");
          console.error(e);
        }
      }
      resolve(res);
    }, function (error) {
      try {
        this$1$1._actionSubscribers
          .filter(function (sub) { return sub.error; })
          .forEach(function (sub) { return sub.error(action, this$1$1.state, error); });
      } catch (e) {
        if ((process.env.NODE_ENV !== 'production')) {
          console.warn("[vuex] error in error action subscribers: ");
          console.error(e);
        }
      }
      reject(error);
    });
  })
};
Store.prototype.commit = function commit (_type, _payload, _options) {
    var this$1$1 = this;
  // check object-style commit
  var ref = unifyObjectStyle(_type, _payload, _options);
    var type = ref.type;
    var payload = ref.payload;
    var options = ref.options;
  var mutation = { type: type, payload: payload };
  var entry = this._mutations[type];
  if (!entry) {
    if ((process.env.NODE_ENV !== 'production')) {
      console.error(("[vuex] unknown mutation type: " + type));
    }
    return
  }
  this._withCommit(function () {
    entry.forEach(function commitIterator (handler) {
      handler(payload);
    });
  });
  this._subscribers
    .slice() // shallow copy to prevent iterator invalidation if subscriber synchronously calls unsubscribe
    .forEach(function (sub) { return sub(mutation, this$1$1.state); });
  if (
    (process.env.NODE_ENV !== 'production') &&
    options && options.silent
  ) {
    console.warn(
      "[vuex] mutation type: " + type + ". Silent option has been removed. " +
      'Use the filter functionality in the vue-devtools'
    );
  }
};