const obj = { 
  name: {
    first:'first-Name1',
    last:'last-name1',
  },
  birthday: {
    year:1800,
    month:10,
    day:10,
  },
  userName: 'User1',
};
const {name:{first,...pl1}, birthday:{year,...pl2}, userName} = obj;
console.log(pl1); //{"last": "last-name1"}
console.log(pl2); //{"month": "10", "day": "10"}
console.log(userName); //"User1"