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 original objects that were in that array.
This is the way I have done it. However, being new to JavaScript I want to make sure this is a good approach.
Is there a better way to do this?
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) =>
{
return Object.assign({}, u);
}
)
.map(
(u) =>
{
u.approved = true;
return u;
}
);
console.log('New users2 array of objects:')
console.log(users2);
console.log('This was original users array is untouched:')
console.log(users);
Output:
New users2 array of objects:
[ { id: 1, name: 'Jack', approved: true },
{ id: 2, name: 'Bill', approved: true },
{ id: 3, name: 'Rick', approved: true },
{ id: 4, name: 'Rick', approved: true } ]
This was original users array is untouched:
[ { id: 1, name: 'Jack', approved: false },
{ id: 2, name: 'Bill', approved: true },
{ id: 3, name: 'Rick', approved: false },
{ id: 4, name: 'Rick', approved: true } ]
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);
.as-console-wrapper { max-height: 100% !important; top: 0; }
UPDATE with spreading properties.
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 => ({ ...u, approved: true })); console.log(users2); console.log(users);
.as-console-wrapper { max-height: 100% !important; top: 0; }
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;
});
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));
There are a few ways to copy a array in javascript, i believed that the most used are:
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"]
In React JS
I tried most ways of copying and modifying the newly copied array but it still modified the original array. The methods I tried are slice
Array.from
for loop
spread operator
, all this ended up modifying the original array. The solution was, stringify
the original array and assign it to a new variable, then parse
the variable to get a fresh copy without reference as stated by @Roman Yakoviv above.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.