Copy array of objects and make changes without modifying original array

Question

I have an array of objects. I would like to deep copy the array of objects and make some changes to each object. I want to do this without modifying the original array or or

Answer 1

For a single pass, you could use Object.assign with the changed property as well.

const users = [{ id: 1, name: 'Jack', approved: false }, { id: 2, name: 'Bill', approved: true }, { id: 3, name: 'Rick', approved: false }, { id: 4, name: 'Rick', approved: true }];
const users2 = users.map(u => Object.assign({}, u, { approved: true }));

console.log(users2);
console.log(users);

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Answer 2

There are a few ways to copy a array in javascript, i believed that the most used are:

• slice()
• Array.from()

The slice function will return a portion (or all content) of a given array as a new array, based at a begin and end index (begin and end index are optional):

const a = [1,2,3,4,5,6,7,8,9]
/*
* Only begin index
*/
const b = a.slice(2)
console.log(b) //Will Print [3,4,5,6,7,8,9]
/*
* Begin index and end index
*/
const c = a.slice(5,8)
console.log(c) //Will Print [6,7,8]
/*
* No indexes provided
*/
const d = a.slice()
console.log(d) //Will print [1,2,3,4,5,6,7,8,9]

Array.from() is a function that will create a new array from an array-like or iterable parameters.

const a = Array.from('bar');
console.log(a) //Will Print ["b","a","r"]
const b = ["for","bar"];
const c = Array.from(b);
console.log(c) //Will print  ["for","bar"]

More about slice

More about Array.from()

Answer 3

I prefer JSON.stringify and JSON.parse

var users = [ { id: 1, name: 'Jack', approved: false },
{ id: 2, name: 'Bill', approved: true },
{ id: 3, name: 'Rick', approved: false },
{ id: 4, name: 'Rick', approved: true } ];

// user2 will be copy of array users without reference
var users2 = JSON.parse(JSON.stringify(users));

Answer 4

Yes that looks good. You could also perform the modification when you are cloning, in order to avoid mapping over the array twice.

const users2 = users.map((u) => {
    const copiedUser = Object.assign({}, u);
    copiedUser.approved = true;
    return copiedUser;
});