feat: add outro option to unmount

[Rich-Harris]

Just an experiment. Supersedes #9056. If you call unmount(component, { outro: true }) then the component's outro transitions will play before the DOM is removed. (You can't 'remount' the component during this time, unmounting is a one-way street.) unmount now returns a Promise.

Demo here.

Notes:

• in the demo the fly transition needs the global modifier in order for the intro to work (but only in the playground, works fine in local testing). That seems odd?

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14540-svelte.vercel.app/

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[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14540

[Serator]

You can't 'remount' the component during this time, unmounting is a one-way street.

@Rich-Harris Is there any chance of changing this behavior? In other words, is it possible to make both animations work synchronously in this example?

[Rich-Harris]

No, that would make things vastly more complicated for no real reason