useMap()function

Create a mutable Map that persists for the lifetime of the component.

• The same Map instance is returned on every render; mutations are not reactive (won't trigger a re-render).

Create a mutable Map that persists for the lifetime of the component. The same Map instance is returned on every render, so it is safe to read from and write to across renders without triggering reconstruction.

useMap does not re-render the component when the map is mutated — it is a stable scratch container, not reactive state. Use it for caches, lookup tables, or per-key bookkeeping that lives alongside a component.

Usage

import { useMap } from "shelving/react";

function Gallery({ ids }: { ids: string[] }) {
  const seen = useMap<string, boolean>(); // Same Map on every render.
  return <>{ids.map(id => {
    const isNew = !seen.has(id);
    seen.set(id, true);
    return <Thumbnail key={id} id={id} highlight={isNew} />;
  })}</>;
}