const itemList = [1, 2, 3];
const additionalItemList = [5, 6];
​
const newItemList = [...itemList, 4, ...additionalItemList];
​
console.log(newItemList); // [1, 2, 3, 4, 5, 6]

const user = {
    firstName: 'Foo',
    lastName: 'BAR',
    email: '[email protected]'
};
​
const newUser = {
    ...user,
    email: '[email protected]',
    phoneNumber: '+6 12 34 56 78'
};
​
console.log(newUser);
// {
//    firstName: 'Foo',
//    lastName: 'BAR',
//    email: '[email protected]',
//    phoneNumber: '+6 12 34 56 78'
//}