js中proxy代理

<script>
    var user = {}
    let proxy = new Proxy(user, {
       get: function(target, propkey) {
          console.log(target, propkey);
          return propkey
       },
       set: function(target, propkey, value) {
          if(propkey=="age"){
             if(!Number.isInteger(value)){
                throw new TypeError("The age is not an integger")
             }
             if(value>=200){
                throw new RangeError("The age seem invalid")
             }
          }
          target[propkey]=value
       }
    })
    proxy.count = 100
    proxy.age=10
    console.log(proxy.age);
</script>