feat: add $state.is rune

[trueadm]

This PR adds the $state.is rune. Fixes #11403.

Sometimes you might need to deal with the equality of two values, where one of the objects might have been wrapped in a with a $state proxy,
you can use $state.is to check if the two values are the same.

<script>
  let state = $state({});
  let object = {};

  state.object = object;

  console.log(state.object === object); // false because of the $state proxy

  console.log($state.is(state.object, object)); // true
</script>

This is handy when you might want to check if the object exists within a deeply reactive object/array.

[changeset-bot]

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Latest commit: c915f59

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[7nik]

For arrays, isn't

let item = $state(maybeRawItem);
let index = array.indexOf(item);

better than

let index = array.findIndex((item) => $state.is(item, maybeRawItem));

?
But the docs don't mention the first approach.

[trueadm]

For arrays, isn't

let item = $state(maybeRawItem);
let index = array.indexOf(item);

better than

let index = array.findIndex((item) => $state.is(item, maybeRawItem));

? But the docs don't mention the first approach.

How do you mean? The first example won’t work?

[7nik]

The first example is better for performance, but not mentioning it may force people to use the second approach.

[trueadm]

The first example is better for performance, but not mentioning it may force people to use the second approach.

They should use the second approach here though?

[7nik]

I doubt that many people are aware of

let foo = {};
$state(foo) == $state(foo); // true

and even may think the opposite and thus assume array.indexOf($state(foo)) won't work.

[trueadm]

I doubt that many people are aware of

let foo = {};
$state(foo) == $state(foo); // true

and even may think the opposite and thus assume array.indexOf($state(foo)) won't work.

That’s what #11610 addresses

[7nik]

So, if somebody carefully reads the docs and writes array.findIndex((item) => $state.is(item, foo)), will #11610 warn them to use array.indexOf($state(foo)) instead?

[trueadm]

So, if somebody carefully reads the docs and writes array.findIndex((item) => $state.is(item, foo)), will #11610 warn them to use array.indexOf($state(foo)) instead?

No, because that's invalid usage of the $state rune. They should be using findIndex here instead. That's my entire point. If they are working with things that are both state, they don't get a warning, if they do then the warning suggests they should refactor to use something like findIndex as they need to incorporate $state.is.

[Nelhoa]

I don’t understand. Then this should not work as expected ?

class MyClass {}

let a = new MyClass()
let b = new MyClass()
let c = $state([a, b])

console.log(c[0] === a) // log 'true' as expected

But it works (REPL).

Not sure to get the point where $state.is() is usefull then.

[7nik]

Only POJOs are proxied. Class instances aren't.