pagination-with-dots.ts

const MAX_PAGES_BLOCK = 3;
const SIDE_PAGE_COUNT = (MAX_PAGES_BLOCK - 1) / 2;

getPages() {
  if (this.totalPages <= MAX_PAGES_BLOCK + 1) {
    return this.range(1, this.totalPages);
  }

  const leftSidePages = this.getLeftSidePages();
  const rightSidePages = this.getRightSidePages();
  console.log(leftSidePages, rightSidePages);

  return leftSidePages.concat([this.currentPage]).concat(rightSidePages);
}

getLeftSidePages(): number[] {
  const leftShiftedPage = this.currentPage - MAX_PAGES_BLOCK;

  if (leftShiftedPage < 0) {
    return this.range(1, this.currentPage - 1);
  }

  if (leftShiftedPage >= 0) {
    const correction =
      this.currentPage === this.totalPages ? SIDE_PAGE_COUNT : 0;

    return [1]
      .concat(leftShiftedPage === 0 ? [] : [0])
      .concat(
        this.range(
          this.currentPage - SIDE_PAGE_COUNT - correction,
          this.currentPage - 1,
        ),
      );
  }
}

getRightSidePages(): number[] {
  const rightShiftedPage = this.currentPage + MAX_PAGES_BLOCK;

  if (rightShiftedPage > this.totalPages) {
    return this.range(this.currentPage + 1, this.totalPages);
  }

  if (rightShiftedPage <= this.totalPages) {
    const correction = this.currentPage === 1 ? SIDE_PAGE_COUNT : 0;

    return this.range(
      this.currentPage + 1,
      this.currentPage + SIDE_PAGE_COUNT + correction,
    )
      .concat(rightShiftedPage > this.totalPages ? [] : [0])
      .concat([this.totalPages]);
  }
}

range(start: number, end: number): number[] {
  return Array.from(Array(end - start + 1), (_, index) => index + start);
}

getTotalPages(): number {
  return Math.ceil(this.length / this.pageSize);
}