mapState

store.js

import Vue from 'vue'
import Vuex from 'vuex'
Vue.use(Vuex)
const store = new Vuex.Store({
  state: {
    count: 0
  },
  mutations: {
    increment (state) {
      state.count++
    },
    decrement (state) {
      state.count--
    }
  },
  actions: {
    increment (context) {
      context.commit('increment')
    },
    decrement (context) {
      context.commit('decrement')
    }
  },
  getters: {
    odd:state => state.count
  }
})
export default store

组件：