A useful utility function to paginate using a page based method

paginate.ts

export interface PaginationOptions {
  totalItems: number;
  currentPage?: number;
  pageSize?: number;
  maxPages?: number;
}
function paginate(options: PaginationOptions) {
  const totalItems = options.totalItems || 1;
  let currentPage = options.currentPage || 1;
  const pageSize = options.pageSize || 10;
  const maxPages = options.maxPages || 1;
  // calculate total pages
  const totalPages = Math.ceil(totalItems / pageSize);

  // ensure current page isn't out of range
  if (currentPage < 1) {
    currentPage = 1;
  } else if (currentPage > totalPages) {
    currentPage = totalPages;
  }

  let startPage: number, endPage: number;
  if (totalPages <= maxPages) {
    // total pages less than max so show all pages
    startPage = 1;
    endPage = totalPages;
  } else {
    // total pages more than max so calculate start and end pages
    const maxPagesBeforeCurrentPage = Math.floor(maxPages / 2);
    const maxPagesAfterCurrentPage = Math.ceil(maxPages / 2) - 1;
    if (currentPage <= maxPagesBeforeCurrentPage) {
      // current page near the start
      startPage = 1;
      endPage = maxPages;
    } else if (currentPage + maxPagesAfterCurrentPage >= totalPages) {
      // current page near the end
      startPage = totalPages - maxPages + 1;
      endPage = totalPages;
    } else {
      // current page somewhere in the middle
      startPage = currentPage - maxPagesBeforeCurrentPage;
      endPage = currentPage + maxPagesAfterCurrentPage;
    }
  }

  // calculate start and end item indexes
  const startIndex = (currentPage - 1) * pageSize;
  const endIndex = Math.min(startIndex + pageSize - 1, totalItems - 1);

  // create an array of pages to ng-repeat in the pager control
  const pages = Array.from(Array(endPage + 1 - startPage).keys()).map((i) => startPage + i);

  // return object with all pager properties required by the view
  return {
    totalItems: totalItems,
    currentPage: currentPage,
    pageSize: pageSize,
    totalPages: totalPages,
    startPage: startPage,
    endPage: endPage,
    startIndex: startIndex,
    endIndex: endIndex,
    pages: pages
  };
}

export default paginate;