Generate pagination number

paginationAlgorithm.js

/**
 * Generate pagination.
 * @param {number} current Current page.
 * @param {number} last Last page.
 * @param {number} width width.
 * @returns {Array} Returns array of pages.
 */

const paginationGenerator = (current, last, width = 2) => {
  const left = current - width;
  const right = current + width + 1;
  const range = [];
  const rangeWithDots = [];
  let l;

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

  range.forEach(i => {
    if (l) {
      if (i - l === 2) {
        rangeWithDots.push(l + 1);
      } else if (i - l !== 1) {
        rangeWithDots.push('...');
      }
    }
    rangeWithDots.push(i);
    l = i;
  });

  return rangeWithDots;
};

/*
Test Result:

Current page 1: 1,2,3,4,...,30
Current page 2: 1,2,3,4,5,...,30
Current page 3: 1,2,3,4,5,6,...,30
Current page 4: 1,2,3,4,5,6,7,...,30
Current page 5: 1,2,3,4,5,6,7,8,...,30
Current page 6: 1,...,4,5,6,7,8,9,...,30
Current page 7: 1,...,5,6,7,8,9,10,...,30
Current page 8: 1,...,6,7,8,9,10,11,...,30
Current page 9: 1,...,7,8,9,10,11,12,...,30
Current page 10: 1,...,8,9,10,11,12,13,...,30
Current page 11: 1,...,9,10,11,12,13,14,...,30
Current page 12: 1,...,10,11,12,13,14,15,...,30
Current page 13: 1,...,11,12,13,14,15,16,...,30
Current page 14: 1,...,12,13,14,15,16,17,...,30
Current page 15: 1,...,13,14,15,16,17,18,...,30
Current page 16: 1,...,14,15,16,17,18,19,...,30
Current page 17: 1,...,15,16,17,18,19,20,...,30
Current page 18: 1,...,16,17,18,19,20,21,...,30
Current page 19: 1,...,17,18,19,20,21,22,...,30
Current page 20: 1,...,18,19,20,21,22,23,...,30
Current page 21: 1,...,19,20,21,22,23,24,...,30
Current page 22: 1,...,20,21,22,23,24,25,...,30
Current page 23: 1,...,21,22,23,24,25,26,...,30
Current page 24: 1,...,22,23,24,25,26,27,...,30
Current page 25: 1,...,23,24,25,26,27,28,29,30
Current page 26: 1,...,24,25,26,27,28,29,30
Current page 27: 1,...,25,26,27,28,29,30
Current page 28: 1,...,26,27,28,29,30
Current page 29: 1,...,27,28,29,30
Current page 30: 1,...,28,29,30
*/