let a = {
  name: "Hobby",
  hobby: {
    sport: 'tennis',
    game: 'switch'
  }
};

const b = Object.assign({}, a)

a.hobby.game = 'ps5'

console.log('a:', a)
console.log('b:', b)
console.log('a === b', a===b)

/* console 結果
a: {
  name: "Hobby",
  hobby: {
    sport: 'tennis',
    game: 'ps5'
  }
}

b: {
  name: "Hobby",
  hobby: {
    sport: 'tennis',
    game: 'ps5'
  }
}

a === b false
*/