A set of JS functions that help in implementing paging.

paging-utils.js

import range from 'lodash/range';

/**
 * Returns the items in a given page.
 * @template T
 * @param {number} offset The index offset based on the given `pageIndex`
 * (precomputed from `calcOffset`).
 * @param {number} itemsPerPage The number of items per page.
 * @param {T[]} items The array of items.
 */
export function getPageItems(offset, itemsPerPage, items) {
  return items.slice(offset, offset + itemsPerPage);
}

/**
 * Calculates the number of pages.
 * @template T
 * @param {number} itemsPerPage The number of items per page.
 * @param {T[]} items The array of items.
 */
export function calcPageCount(itemsPerPage, items) {
  return Math.ceil(items.length / itemsPerPage);
}

/**
 * Calculates the index offset.
 * @param {number} pageIndex The page number (starting from zero).
 * @param {number} itemsPerPage The number of items per page.
 */
export function calcOffset(pageIndex, itemsPerPage) {
  return pageIndex * itemsPerPage;
}

/**
 * Calculates the page numbers given the page count.
 * @param {number} pageCount The number of pages available (precomputed from
 * `calcPageCount`).
 */
export function calcPageNumbers(pageCount) {
  return range(1, pageCount + 1);
}