// moduleA.js
const state = {
  username: ''
}

const mutations = {
  SET_USERNAME: (state, username) => {
    state.username = username
  }
}

const actions = {
  getUsername ({ commit }, username) {
    commit('SET_USERNAME', username)
  }
}

export default {
  namespaced: true,
  state,
  mutations,
  actions
}

// 页面（组件）中使用
import { mapState, mapActions } from 'vuex'
export default {
  computed: {
    ...mapState({
      username: state => state.moduleA.username // moduleA中的state
    })
  },
  methods: {
    ...mapActions({
      getUsername: 'moduleA/getUsername' // moduleA中的Actions
    })
  }
}