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feat(ui): floating back-to-top button on long scrollable pages

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A reusable BackToTop fades in once the active page's <main> is scrolled past ~600px and
smooth-scrolls it back to the top. Rendered once at the App root, portaled to <body> for
viewport-fixed placement (bottom-right, below the chat dock), and re-binds to the live <main> on
navigation (page or channel change) so it works on every scrollable page incl. the channel page.
EN/HU/DE.
This commit is contained in:
npeter83 2026-06-30 05:02:42 +02:00
parent f25d0768a1
commit 6b47b0d357
5 changed files with 53 additions and 3 deletions
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44
frontend/src/components/BackToTop.tsx Normal file
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import { useEffect, useRef, useState } from "react";
import { createPortal } from "react-dom";
import { ArrowUp } from "lucide-react";
import { useTranslation } from "react-i18next";
// A floating "back to top" button that fades in once the current page's scroll container is
// scrolled past a threshold, and smooth-scrolls it back to the top. Every page scrolls inside its
// own <main class="overflow-y-auto"> (the normal pages share App's; the channel page has its own),
// so it targets the live <main> and re-binds whenever `dep` changes (i.e. on navigation). Portaled
// to <body> so its fixed position is viewport-relative regardless of transformed ancestors.
export default function BackToTop({ dep, threshold = 600 }: { dep?: unknown; threshold?: number }) {
const { t } = useTranslation();
const [show, setShow] = useState(false);
const scrollerRef = useRef<HTMLElement | null>(null);
useEffect(() => {
const el = document.querySelector("main");
scrollerRef.current = el;
if (!el) {
setShow(false);
return;
}
const onScroll = () => setShow(el.scrollTop > threshold);
onScroll(); // a freshly-bound page starts at the top → hidden
el.addEventListener("scroll", onScroll, { passive: true });
return () => el.removeEventListener("scroll", onScroll);
}, [dep, threshold]);
const toTop = () => scrollerRef.current?.scrollTo({ top: 0, behavior: "smooth" });
return createPortal(
<button
onClick={toTop}
aria-label={t("common.backToTop")}
title={t("common.backToTop")}
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 ${
show ? "opacity-100 translate-y-0" : "opacity-0 translate-y-3 pointer-events-none"
}`}
>
<ArrowUp className="w-5 h-5" />
</button>,
document.body
);
}