Export scroll position props in scroll area

[basselalsayed]

I had a use case where I needed to know the current scroll position as I was doing some calculations on the position of an element within the scroll area, and I ended up doing this: thought it might be a useful feature for other people so leaving here! Not sure if the two way binding is necessary but would be easy to add I think.

<script lang="ts">
	import { onMount } from "svelte";
	import { ScrollArea as ScrollAreaPrimitive } from "bits-ui";
	import { Scrollbar } from "./index.js";
	import { cn } from "$lib/utils.js";

	type $$Props = ScrollAreaPrimitive.Props & {
		orientation?: "vertical" | "horizontal" | "both";
		scrollbarXClasses?: string;
		scrollbarYClasses?: string;
	};

	let className: $$Props["class"] = undefined;
	export { className as class };
	export let orientation = "vertical";
	export let scrollbarXClasses: string = "";
	export let scrollbarYClasses: string = "";
	export let scrollLeft: number = 0;
	export let scrollTop: number = 0;

	let scrollViewport: HTMLDivElement;

	onMount(() => {
		function onScroll(e: Event) {
			const viewPortEl = e.target as HTMLDivElement;
			scrollLeft = viewPortEl.scrollLeft;
			scrollTop = viewPortEl.scrollTop;
		}

		scrollViewport.addEventListener("scroll", onScroll);

		return () => {
			scrollViewport.removeEventListener("scroll", onScroll);
		};
	});
</script>

<ScrollAreaPrimitive.Root {...$$restProps} class={cn("relative overflow-hidden", className)}>
	<ScrollAreaPrimitive.Viewport bind:el={scrollViewport} class="h-full w-full rounded-[inherit]">
		<ScrollAreaPrimitive.Content>
			<slot />
		</ScrollAreaPrimitive.Content>
	</ScrollAreaPrimitive.Viewport>
	{#if orientation === "vertical" || orientation === "both"}
		<Scrollbar orientation="vertical" class={scrollbarYClasses} />
	{/if}
	{#if orientation === "horizontal" || orientation === "both"}
		<Scrollbar orientation="horizontal" class={scrollbarXClasses} />
	{/if}
	<ScrollAreaPrimitive.Corner />
</ScrollAreaPrimitive.Root>