Vuex：Mutation常量类型

export const INCREMENT = ‘increment‘

//1 导入  
import {INCREMENT} from "./store/mutations-types"

//2 使用
//methods:{
      addition(){
        this.$store.commit(INCREMENT)
      },
      subtraction(){
        this.$store.commit(‘decrement‘)
      }
    }

//1导入 
import * as myMutations  from "@/store/mutations-types"

mutations:{
    //方法 默认带state参数
    [myMutations.INCREMENT](state){
      state.counter++
    },
    decrement(state){
      state.counter--
    }
  },