Javascript push array into another array

Question

Is there any difference between the following code(with/without spread operator)?

let result = [];
let arr1 = [1,2,3];

result.push(arr1)
result.push([...arr1])

Try changing arr1 (eg: arr[0]++), and log the result, you'll see the first gets changed as it's a reference — Nick Parsons
– Nick Parsons, Commented Mar 20, 2021 at 0:34

CertainPerformance · Accepted Answer · 2021-03-20 00:33:51Z

5

In the first, without spreading, any modifications to the array at the 0th position in result will result in a change to the original arr1 as well, and vice versa.

If you spread the array while pushing, though, such changes will not occur; the two arrays (one in arr1, one in result[0]) will be completely independent.

let result = [];
let arr1 = [1,2,3];

result.push(arr1)

arr1[1] = 999;
console.log(result);

let result = [];
let arr1 = [1,2,3];

result.push([...arr1])

arr1[1] = 999;
console.log(result);

answered Mar 20, 2021 at 0:33

CertainPerformance

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