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pnpm add https://pkg.pr.new/svelte@15512

Will this have any unwanted impact on transitions? (TBH I'm not even sure if we want to run transitions on moved within an array, or if they do right now)

I don't think this will impact transitions, since they are executed before/after the node is deleted/added.
I made some stuff on playground without impact...

But, I also tested the demo-site :https://state-preserving-atomic-move.glitch.me/
And the "popover" scenario crashes Chrome... :/

Maybe it would be better to wait until it is a little more stable.

We only want to usemoveBefore on post mount operations. Otherwise, there are issues with web component FWIW where they don't fire the connected callback if used on mount. Context:facebook/react#32567

The "no side effects" comment is an indicator for bundlers that a function is pure.

We only want to usemoveBefore on post mount operations.

I think it's fine : if I'm not mistaken it's only used on thereconcille() of {#each}` blocks to move existing element.

The "no side effects" comment is an indicator for bundlers that a function is pure.

So I suppose this is not the case here, since the DOM is modified...

I'm going to close this because I'm quite certain we shouldn't do this. It will make bugsmore likely, not less, because it means that people will see stuff working in Chrome and assume it works everywhere. It's much better if people are forced to solve these issues in a cross-browser way — Svelte should avoid having different behaviour between different browsers.