Function zoomBy

frontend/src/maps.tsx:270–277

(delta: number)

  }, [challenge, config, selectedCenter]);

  function zoomBy(delta: number) {
    const holder = mapRef.current;
    if (!holder) return;
    const { map } = holder;
    const nextZoom = Math.max(3, Math.min(20, map.getZoom() + delta));
    map.setZoom(nextZoom);
    setZoom(nextZoom);
  }

  useEffect(() => {
    const holder = mapRef.current;