const user = {
  profile: {
    settings: {
      theme: 'dark',
      notifications: null
    }
  }
};

const result1 = user?.profile?.settings?.theme;
const result2 = user?.profile?.settings?.notifications?.email;
const result3 = user?.profile?.preferences?.language ?? 'en';
const result4 = user?.profile?.settings?.notifications?.push?.('test');

console.log(result1, result2, result3, result4);

const original = {
  name: 'Sarah',
  hobbies: ['reading', 'coding'],
  address: { city: 'Portland', zip: 97201 }
};

const shallow = { ...original };
const deep = JSON.parse(JSON.stringify(original));

shallow.name = 'Emma';
shallow.hobbies.push('hiking');
shallow.address.city = 'Seattle';

deep.hobbies.push('swimming');
deep.address.zip = 98101;

console.log(original.hobbies.length, original.address.city);