Javascript +ES: Is there any difference between [...arr] and arr?

Question

Consider a scenario where in you are trying to iterate over a const array. Would there be any difference between

[...arr].forEach((elem) => {
  // your operations
});

and

 arr.forEach((elem) => {
   // your operations
 });

Can these two be used interchangeably?

Yes, they can. I don't see why you would want to use the first expression rather than the second one. — Blackhole, Jul 23 '18 at 14:19
Yes!! a constant array will only have the address as constant, you can still change/add elements to it. But when you use the spread operator, you don't touch the original array — Ashish Ranjan, Jul 23 '18 at 14:19

score 4 · Accepted Answer · answered Jul 23 '18 at 14:22

It will make a copy of the array. If the callback function would use the array parameter and it would modify it, that would make a difference. E.g.:
```
[...arr].forEach((val, i, a) => a.push(val))
```
If arr is not an array but an array-like, it will turn it into an array and thereby allow you to forEach over it. E.g.:
```
[...document.getElementsByTagName('p')].forEach(p => console.log(p))
```

1 Answers1