addRemoveField.js

var person = {
  firstName: 'Hoang',
  lastName: 'Pham',
  showName: function() {
    console.log(this.firstName + ' ' + this.lastName);
  }
};

delete person.lastName; // Xóa trường lastName
person.lName = 'Just adding'; // Thêm trường lName

console.log(person.lastName); // undefined
console.log(person.lName); // Just adding