Rule proposal: `prefer-change-array-by-copy`

[fisker]

"Change Array by copy" proposal

Fail

array.reverse();

array.sort();

const array = [...foo];
array.splice(0, 1);

const array = [...foo];
array[1] = 'changed';

Pass

array = array.toReversed();

array = array.toSorted();

const array = foo.toSpliced(0, 1);

const array = foo.with(1, 'changed');

[sindresorhus]

Good idea. This will have to wait until it's shipping in a browser/Node.js version. The naming of the methods are not final.

[fregante]

I don't know, if the intent is to replace the existing variable, I don't particularly see an advantage in using with*

For example:

list.splice(1, 3); // Drop unwanted items

but also

const removedItems = list.splice(1, 3); // Drop unwanted items and save them elsewhere

However I agree that this should be an error:

const newArray = old.reverse()

[fisker]

The proposal has updated, see https://github.com/tc39/proposal-change-array-by-copy/commit/752e576db3d55e9d1d80a97df1f1e54c26ffbd7f

• withReversed -> toReversed
• withSorted -> toSorted
• withSpliced -> toSpliced
• withAt -> with

[fisker]

Change Array by Copy to Stage 3 per 2022.03.30 TC39

[fregante]

One pattern that I've been using is to clone arrays in the function parameters and I hope it can be preserved. I think the same thing applies to array destructuring.

Before

function foo(originalBar) {
	const bar = [...originalBar];
	return bar;
}

After

function foo([...bar] /* Shallow bar clone*/) {
	return bar;
}

[Cherry]

This hit Stage 4 today, so we should see it start shipping soon more than likely 👀

[fisker]

Maybe we should split this into separate rules, to make rules easier to maintain.

• prefer-array-to-reversed
• prefer-array-to-sorted
• prefer-array-to-spliced
• prefer-array-with

[joealden]

With the release of Firefox 115, these methods are now available in all major browsers!

[klimashkin]

85%+ support according to caniuse

[silverwind]

Should also detect cases where Array.from is used to shallow-clone, e.g. when unicorn/prefer-spread is disabled:

Fail

const sorted = Array.from(arr).sort();

Pass

const sorted = arr.toSorted();

[markcarroll]

Bump. @sindresorhus this has been around for a few months in all browsers now and in Node 20, so any chance we could get this in now?

[sindresorhus]

This is accepted. Pull requests are welcome :)