add in object by for in in javascript

Question

I am new in javascript I have object. When I try to add the city, it doesn't appear in the message. This object show us the detail person. but when I want to put city (forExample) it doesn't show in message

let person = {

  name: 'Sam',
  age: 30,
  employed: true,
  is_maried: false

}

and

for (let key in person){


  let massage = `key: ${key} and the value is ${person[key]}`;
  //this to give you the key name and the value in on line

  if (key in person === 'city'){

    person.city = 'NY';


  }else if (!(key in person !== 'city')){

      person.city = 'UK';

  }

console.log(massage);
}