new Vue({
  data(){
    return{
      loading:true
    }
  },
  router,
  store,
  render: h => h(App)
}).$mount('#app')

created(){
   console.log(this.$root.loading) //获取loading的值
}

created(){
   this.$root.loading = false; //设置loading的属性
}

mounted () {
  document.body.classList.add('bg-light')
},
destroyed () {
  document.body.classList.remove('bg-light')
}

vue

mounted () {
  document.body.classList.add('bg-light', 'login')
},
destroyed () {
  document.body.classList.remove('bg-light', 'login')
},

javascript

{
  path: '/login',
  name: 'login',
  component: Login,
  meta: { bodyClass: 'bg-light' }
}