Pagination Algorithm in Typescript

typescript-pagination.ts

  static getPagination(currentPage: number, totalPages: number): string[] {
    const delta = 2,
      left = currentPage - delta,
      right = currentPage + delta + 1,
      range: number[] = [],
      rangeString: string[] = [];
    let tmp = 0;

    for (let i = 1; i <= totalPages; i++) {
      if (i == 1 || i == totalPages || i >= left && i < right) {
        range.push(i);
      }
    }

    for (const i of range) {
      if (tmp) {
        if (i - tmp === 2) {
          rangeString.push((tmp + 1).toString());
        } else if (i - tmp !== 1) {
          rangeString.push('...');
        }
      }
      rangeString.push(i.toString());
      tmp = i;
    }

    return rangeString;
  }
  
  /* 
Outputs:
[1, 2, 3, "...", 10]
[1, "...", 8, 9, 10, 11, 12, "...", 20]
[1, "...", 8, 9, 10]
*/