rc-virtual-list/es/hooks/useGetSize.js

React Virtual List Component

import _slicedToArray from "@babel/runtime/helpers/esm/slicedToArray";
import * as React from 'react';

/**
 * Size info need loop query for the `heights` which will has the perf issue.
 * Let cache result for each render phase.
 */
export function useGetSize(mergedData, getKey, heights, itemHeight) {
  var _React$useMemo = React.useMemo(function () {
      return [new Map(), []];
    }, [mergedData, heights.id, itemHeight]),
    _React$useMemo2 = _slicedToArray(_React$useMemo, 2),
    key2Index = _React$useMemo2[0],
    bottomList = _React$useMemo2[1];
  var getSize = function getSize(startKey) {
    var endKey = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : startKey;
    // Get from cache first
    var startIndex = key2Index.get(startKey);
    var endIndex = key2Index.get(endKey);

    // Loop to fill the cache
    if (startIndex === undefined || endIndex === undefined) {
      var dataLen = mergedData.length;
      for (var i = bottomList.length; i < dataLen; i += 1) {
        var _heights$get;
        var item = mergedData[i];
        var key = getKey(item);
        key2Index.set(key, i);
        var cacheHeight = (_heights$get = heights.get(key)) !== null && _heights$get !== void 0 ? _heights$get : itemHeight;
        bottomList[i] = (bottomList[i - 1] || 0) + cacheHeight;
        if (key === startKey) {
          startIndex = i;
        }
        if (key === endKey) {
          endIndex = i;
        }
        if (startIndex !== undefined && endIndex !== undefined) {
          break;
        }
      }
    }
    return {
      top: bottomList[startIndex - 1] || 0,
      bottom: bottomList[endIndex]
    };
  };
  return getSize;
}