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])

• Nick Parsons: Try changing arr1 (eg: arr[0]++), and log the result, you'll see the first gets changed as it's a reference

Answer 1

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);