问模块未找到:错误:无法解析/myapp/src/store中的“vuex”

EN

./src/store/index.js
Module not found: Error: Can't resolve 'vuex' in '/myapp/src/store'

// package.json

"dependencies": {
  "axios": "^0.19.2",
  "core-js": "^2.6.5",
  "vue": "^2.6.10",
  "vue-router": "^3.4.2",
  "vuex": "^3.5.1"
},

// src/store/index.js

import Vue from 'vue'
import Vuex from 'vuex'

Vue.use(Vuex)

const store = new Vuex.Store({
  state: {
    userId: "",
    userToken: ""
  },
  mutations: {
    updateUser(state, user) {
      state.userId = user.userId;
      state.userToken = user.userToken;
    }
  },
  actions: {
    auth(context, user) {
      context.commit('updateUser', user);
    }
  },
  modules: {},
})

export default store