// 用localStorage来实现一个预设值
1. 先从localStorage读取，有值则赋给它设初值
const defaultRole = ref(null)
if(process.client){
  let latest = localStorage.getItem("defaultRole")
  console.log(566, "latest", latest)
  if(latest != null){
    defaultRole.value = latest
    console.log(599, "latest")
  }
}   
2. //设置或更新 如果是空值 或是与前值不同，都重新赋值
let latest = localStorage.getItem("defaultRole")
if(latest == null || role != latest){
   localStorage.setItem('defaultRole', role)
   console.log(899, "set lastname")
}