What is the difference between .slice() and directly assigning an array in JavaScript

Question

Can someone explain to me the difference between assigning an array directly, using spread operator and the slice method in JavaScript? For instance:

const a = [1,2,3,4,5];
const b = a;
const c = a.slice();
const d = [...a];

What is the difference between b, c and d arrays ? Has it got something to do with shallow and deep copies?

`a.slice()` and `[...a]` produce shallow copies. `const b = a;` makes `b` point to the same array as `a`. — Unmitigated, Apr 01 '23 at 06:12
Also spread works on any iterable (plus objects), while slice is on Array.prototype (so only works on arrays); and using spread to copy a sparse array will result in undefined elements (rather than empty elements). None of those give you a deep copy, for that you could use `structuredClone`, `JSON.parse(JSON.stringify(x))`, or some other option. — Zac Anger, Apr 01 '23 at 06:16
@Unmitigated, the official documentation of shallow copy says that "A shallow copy of an object is a copy whose properties share the same references (point to the same underlying values) as those of the source object. As a result, when you change either the source or the copy, you may also cause the other object to change too — and so, you may end up causing changes to the source or copy that you don't expect. That behavior contrasts with the behavior of a deep copy, in which the source and copy are completely independent." Doesn't this imply that both arrays c, d are like b (in ref)? — coolest-duck, Apr 01 '23 at 06:22
If you add elements to `a`, it affects `b` but not `c` or `d`. — Unmitigated, Apr 01 '23 at 06:24

score 0 · Answer 1 · answered Apr 01 '23 at 18:47

0

With slice() you can copy a portion of an array.

answered Apr 01 '23 at 18:47

Tania

1 Answers1