将 Vue 2 迁移到 Vue 3，类型错误：Vue 不是构造函数

Question

如何将 Vue 2 语法迁移到 Vue 3，因为我收到以下错误：

类型错误：Vue 不是构造函数。

现在我正在使用 Vue 3：

let app;

firebase.auth().onAuthStateChanged(user => {

  console.log("user", user);

  if (!app) {

    app = new Vue({

      router,

      store,

      render: h => h(App)

    }).$mount("#app");

  }

});

到

import { createApp } from "vue";

const app = createApp({

});

app.mount("#app");

Answer 1

Vue 3、Vuex 4、Vue Router 4 中的代码等效于：import { createApp } from 'vue'import store from './store'import router from './router'import App from './App.vue'let app;firebase.auth().onAuthStateChanged(user => {  console.log("user", user);  app = createApp(App);  app.use(store);  app.use(router);  app.mount("#app");});store.js中的存储语法略有不同：import { createStore } from 'vuex'// now uses `createStore`export default createStore({   state: {},  getters: {},  mutations: {},  actions: {}})以及router.js中的路由器：import { createWebHistory, createRouter } from "vue-router";import Home from "@/views/Home.vue";import About from "@/views/About.vue";const routes = [  {    path: "/",    name: "Home",    component: Home,  },  {    path: "/about",    name: "About",    component: About,  },];const router = createRouter({  history: createWebHistory(),  routes,});export default router;