❗️Что будет на выходе:

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);

Ответ: 3, Seattle

JavaScript test | #JavaScript