45 lines
1.9 KiB
TypeScript
45 lines
1.9 KiB
TypeScript
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import { useEffect, useRef, useState } from "react";
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import { createPortal } from "react-dom";
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import { ArrowUp } from "lucide-react";
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import { useTranslation } from "react-i18next";
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// A floating "back to top" button that fades in once the current page's scroll container is
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// scrolled past a threshold, and smooth-scrolls it back to the top. Every page scrolls inside its
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// own <main class="overflow-y-auto"> (the normal pages share App's; the channel page has its own),
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// so it targets the live <main> and re-binds whenever `dep` changes (i.e. on navigation). Portaled
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// to <body> so its fixed position is viewport-relative regardless of transformed ancestors.
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export default function BackToTop({ dep, threshold = 600 }: { dep?: unknown; threshold?: number }) {
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const { t } = useTranslation();
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const [show, setShow] = useState(false);
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const scrollerRef = useRef<HTMLElement | null>(null);
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useEffect(() => {
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const el = document.querySelector("main");
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scrollerRef.current = el;
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if (!el) {
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setShow(false);
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return;
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}
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const onScroll = () => setShow(el.scrollTop > threshold);
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onScroll(); // a freshly-bound page starts at the top → hidden
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el.addEventListener("scroll", onScroll, { passive: true });
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return () => el.removeEventListener("scroll", onScroll);
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}, [dep, threshold]);
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const toTop = () => scrollerRef.current?.scrollTo({ top: 0, behavior: "smooth" });
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return createPortal(
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<button
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onClick={toTop}
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aria-label={t("common.backToTop")}
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title={t("common.backToTop")}
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className={`fixed bottom-5 right-5 z-30 inline-flex items-center justify-center w-11 h-11 rounded-full bg-card border border-border text-fg shadow-lg hover:border-accent hover:text-accent transition-all duration-200 ${
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show ? "opacity-100 translate-y-0" : "opacity-0 translate-y-3 pointer-events-none"
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}`}
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>
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<ArrowUp className="w-5 h-5" />
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</button>,
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document.body
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);
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}
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