Function useDynamicRowHeight

lib/components/list/useDynamicRowHeight.ts:7–142

({
  defaultRowHeight,
  key
}: {
  defaultRowHeight: number;
  key?: string | number;
})

import type { DynamicRowHeight } from "./types";

export function useDynamicRowHeight({
  defaultRowHeight,
  key
}: {
  defaultRowHeight: number;
  key?: string | number;
}) {
  const [state, setState] = useState<{
    key: string | number | undefined;
    map: Map<number, number>;
  }>({
    key,
    map: new Map()
  });

  if (state.key !== key) {
    setState({
      key,
      map: new Map()
    });
  }

  const { map } = state;

  const getAverageRowHeight = useCallback(() => {
    let totalHeight = 0;

    map.forEach((height) => {
      totalHeight += height;
    });

    if (totalHeight === 0) {
      return defaultRowHeight;
    }

    return totalHeight / map.size;
  }, [defaultRowHeight, map]);

  const getRowHeight = useCallback(
    (index: number) => {
      const measuredHeight = map.get(index);
      if (measuredHeight !== undefined) {
        return measuredHeight;
      }

      // Temporarily store default height in the cache map to avoid scroll jumps if rowProps change
      // Else rowProps changes can impact the average height, and cause rows to shift up or down within the list
      // see github.com/bvaughn/react-window/issues/863
      map.set(index, defaultRowHeight);

      return defaultRowHeight;
    },
    [defaultRowHeight, map]
  );

  const setRowHeight = useCallback((index: number, size: number) => {
    setState((prevState) => {
      if (prevState.map.get(index) === size) {