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offset.simple.tsx
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offset.simple.tsx
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import type { LinksFunction, LoaderArgs } from "@remix-run/node";
import { json } from "@remix-run/node";
import { useFetcher, useLoaderData, useTransition } from "@remix-run/react";
import { useCallback, useEffect, useRef, useState } from "react";
import { useVirtual } from "react-virtual";
import stylesUrl from "~/styles/index.css";
import { getItems } from "~/utils/backend.server";
export const links: LinksFunction = () => [
{ rel: "stylesheet", href: stylesUrl },
];
const LIMIT = 200;
const DATA_OVERSCAN = 40;
const getStartLimit = (searchParams: URLSearchParams) => ({
start: Number(searchParams.get("start") || "0"),
limit: Number(searchParams.get("limit") || LIMIT.toString()),
});
export const loader = async ({ request }: LoaderArgs) => {
const { start, limit } = getStartLimit(new URL(request.url).searchParams);
return json(
{ items: await getItems({ start, limit }) },
{ headers: { "Cache-Control": "public, max-age=120" } },
);
};
export default function Index() {
const data = useLoaderData<typeof loader>();
const [items, setItems] = useState(data.items);
const transition = useTransition();
const fetcher = useFetcher();
const startRef = useRef(0);
const parentRef = useRef<HTMLDivElement>(null);
const rowVirtualizer = useVirtual({
size: items.length,
parentRef,
estimateSize: useCallback(() => 35, []),
initialRect: { width: 0, height: 800 },
});
const [lastVirtualItem] = [...rowVirtualizer.virtualItems].reverse();
if (!lastVirtualItem) {
throw new Error("this should never happen");
}
let newStart = startRef.current;
const upperBoundary = startRef.current + LIMIT - DATA_OVERSCAN;
if (lastVirtualItem.index > upperBoundary) {
// user is scrolling down. Move the window down
newStart = startRef.current + LIMIT;
}
useEffect(() => {
if (newStart === startRef.current) return;
const qs = new URLSearchParams([
["start", String(newStart)],
["limit", String(LIMIT)],
]);
fetcher.load(`/offset/simple?${qs}`);
startRef.current = newStart;
}, [newStart, fetcher]);
useEffect(() => {
if (fetcher.data) {
setItems((prevItems) => [...prevItems, ...fetcher.data.items]);
}
}, [fetcher.data]);
return (
<main>
<h1>Simple Infinite Scrolling (offset={startRef.current})</h1>
<div
ref={parentRef}
className="List"
style={{
height: `800px`,
width: `100%`,
overflow: "auto",
}}
>
<div
style={{
height: `${rowVirtualizer.totalSize}px`,
width: "100%",
position: "relative",
}}
>
{rowVirtualizer.virtualItems.map((virtualRow) => {
const item = items[virtualRow.index];
return (
<div
key={virtualRow.key}
className={`list-item ${
virtualRow.index % 2 ? "list-item--odd" : "list-item--even"
}`}
style={{
position: "absolute",
top: 0,
left: 0,
width: "100%",
height: `${virtualRow.size}px`,
transform: `translateY(${virtualRow.start}px)`,
}}
>
<span>{virtualRow.index}</span>
<span>
{item
? item.value
: transition.state === "loading"
? "Loading more..."
: "Nothing to see here..."}
</span>
</div>
);
})}
</div>
</div>
</main>
);
}