@atlaskit/pagination/dist/es2019/internal/utils/collapse-range.js

Pagination allows you to divide large amounts of content into smaller chunks across multiple pages.

import memoizeOne from 'memoize-one';

// TODO: comma needed after generic declaration below, or the .tsx file thinks
// it is a JSX element. Tidy up in a future refactor.
const collapseRange = (pages, current, {
  max,
  ellipsis,
  transform
}, testId) => {
  const total = pages.length;
  // only need ellipsis if we have more pages than we can display
  const needEllipsis = total > max;
  // show start ellipsis if the current page is further away than max - 4 from the first page
  const hasStartEllipsis = needEllipsis && max - 4 < current;
  // show end ellipsis if the current page is further than total - max + 3 from the last page
  const hasEndEllipsis = needEllipsis && current < total - max + 3;
  const getPageComponents = memoizeOne((startIndex = 0, lastIndex = total) => {
    return pages.slice(startIndex, lastIndex).map((page, index) => transform(page, startIndex + index, testId));
  });
  if (!needEllipsis) {
    return getPageComponents(0, total);
  }
  if (hasStartEllipsis && !hasEndEllipsis) {
    const pageCount = max - 2;
    return [...getPageComponents(0, 1), ellipsis({
      key: 'ellipsis-1',
      testId: testId && `${testId}-ellipsis`,
      from: 2,
      to: total - pageCount
    }), ...getPageComponents(total - pageCount)];
  }
  if (!hasStartEllipsis && hasEndEllipsis) {
    const pageCount = max - 2;
    return [...getPageComponents(0, pageCount), ellipsis({
      key: 'ellipsis-1',
      testId: testId && `${testId}-ellipsis`,
      from: pageCount + 1,
      to: total - 1
    }), ...getPageComponents(total - 1)];
  }
  // we have both start and end ellipsis
  const pageCount = max - 4;
  return [...getPageComponents(0, 1), ellipsis({
    key: 'ellipsis-1',
    testId: testId && `${testId}-ellipsis`,
    from: 2,
    to: current - Math.floor(pageCount / 2)
  }), ...getPageComponents(current - Math.floor(pageCount / 2), current + pageCount - 1), ellipsis({
    key: 'ellipsis-2',
    testId: testId && `${testId}-ellipsis`,
    from: current + 3,
    to: total - 1
  }), ...getPageComponents(total - 1)];
};
export default collapseRange;