fix(useScroll): trigger once onMounted to get correct inital arrivedStates values

[nicooprat]

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Description

Fix #2875

useScroll have incorrect initial values for arrivedStates (bottom & right are false by default) and are not computed if the child is smaller than its parent (can't scroll at all anyway).

Running the demo, it's easy to reproduce: just decrease the child dimensions here

vueuse/packages/core/useScroll/demo.vue

Lines 34 to 35 in 70a7f07

	<div ref="el" class="w-300px h-300px m-auto overflow-scroll bg-gray-500/5 rounded">
	<div class="w-500px h-400px relative">

Before:

After:

Additional context

Following antfu proposition, I just triggered once setArrivedState when the component is first mounted.

Edit: we might also want to watch for element resize for responsive purposes, but I'm not sure how would be the best way to use useResizeObserver here.

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🤖 Generated by Copilot at 2838f20

Improved useScroll function to initialize state and handle errors on mount, and to update state based on element's scroll properties.

🤖 Generated by Copilot at 2838f20

• Import tryOnMounted function from @vueuse/shared to execute callbacks on mount (link)
• Call setArrivedState function with resolved element argument to initialize scroll state on mount (link)

[steklopod]

@antfu this breaks what was working in version 1.5.0:

const { arrivedState } = useScroll(scrollBox)
const { bottom } = toRefs(arrivedState) // <-- ❌ This line produces an error in version 1.6.0 [ but not in 1.5.0 ]