pagination algorithm

computeRange.js

import { isNumber } from 'lodash';

/**
 * Creates an array of page numbers based on the selected page and rangeSize and optionally the last page.
 * Both parameters are used to define what should be visible in the range.
 * When lastPage is provided, the resulting range is frozen within lastPage's boundaries.
 *
 * @param {Number} page The desired page.
 * @param {Number} rangeSize The size of the range to be created.
 * @param {NUmber} lastPage The page used to delimit the max page.
 * @returns An array with range of the affected pages.
 */
export const computeRange = (page = 1, rangeSize = 1, lastPage) => {
  let computedPage = page;

  if (page < 0) {
    return new TypeError('The desired page must be a value bigger than 0.');
  }

  if (rangeSize < 0) {
    return new RangeError('Cannot build a range with a negative value.');
  }

  let threshould = Math.ceil(rangeSize / 2);

  if (isNumber(lastPage) && ((page + rangeSize) > lastPage)) {
    computedPage = (lastPage - threshould) + 1
    if (computedPage > page) computedPage = page;
  }

  return new Array(rangeSize).fill(1).map((irrelevantValue, index) => {
    let currentPageIndex = (computedPage + index + threshould) - rangeSize;
    if (currentPageIndex < index + 1) {
      currentPageIndex = index + 1;
    }
    return currentPageIndex;
  });
};