Vanilla JS improved pagination algorithm

pagination.js

/**
 * Calculates a fixed-length array of pagination display elements,
 * Example return value: [1, "...", 4, 5, 6, "...", 20]
 *
 * Inspired by https://gist.github.com/kottenator/9d936eb3e4e3c3e02598, but re-worked to ensure
 * that the number of display elements stays constant regardless of the current page. Thus, the
 * algorithm mimics the behavior of https://material-ui.com/components/pagination/
 *
 * @param   {number} currentPage
 *          The current page. The rest of the display is oriented around this page.
 * @param   {number} totalPages
 *          The total number of pages available.
 * @param   {number} [displaySize]
 *          The number of display elements.
 *
 * @returns An array of length === displaySize, containing content for the pagination element.
 */

const pagination = (currentPage, totalPages, displaySize = 7) => {
  // do not display more than the total number of pages
  const displaySizeAdj = Math.min(displaySize, totalPages);

  // subtract 1 to leave room for the first and last values
  const displaySizeHalf = Math.floor(displaySizeAdj / 2) - 1;

  // at a minimum, we want a range of [1]
  const range = [1];
  if (totalPages <= 1) {
    return range;
  }

  /* 
  If currentPage is near the center of the range, it will be bounded by +/- (displaySizeHalf - 1)
  As currentPage approaches totalPages, i needs a downward adjustment to ensure 
  range.length = displaySize

  Example: if totalPages = 20, currentPage = 19, 
    we want a range:
      [1, '...', 16, 17, 18, 19, 20]
    rather than:
      [1, '...', 17, 18, 19, 20]
  */
  let i = currentPage - displaySizeHalf;
  i = Math.min(i, totalPages - displaySizeHalf * 2 - 1);

  while (range.length < displaySizeAdj && i !== totalPages) {
    if (i < totalPages && i > 1) {
      range.push(i);
    }
    i++;
  }

  // totalPages is always the last entry
  range[displaySizeAdj - 1] = totalPages;

  // check for starting ellipsis
  if (range[1] !== 2) {
    range[1] = "...";
  }

  // check for ending ellipsis
  if (range[displaySizeAdj - 2] !== totalPages - 1) {
    range[displaySizeAdj - 2] = "...";
  }

  return range;
};

// illustrates function output
const total = 20;
const testValues = [...Array(total + 1).keys()].slice(1);
for (const x in testValues) {
  console.log(
    `pagination(${x}, ${total}) -> ` + pagination(x, total).toString()
  );
}

/* 
pagination(0, 20) -> 1,2,3,4,5,...,20
pagination(1, 20) -> 1,2,3,4,5,...,20
pagination(2, 20) -> 1,2,3,4,5,...,20
pagination(3, 20) -> 1,2,3,4,5,...,20
pagination(4, 20) -> 1,2,3,4,5,...,20
pagination(5, 20) -> 1,...,4,5,6,...,20
pagination(6, 20) -> 1,...,5,6,7,...,20
pagination(7, 20) -> 1,...,6,7,8,...,20
pagination(8, 20) -> 1,...,7,8,9,...,20
pagination(9, 20) -> 1,...,8,9,10,...,20
pagination(10, 20) -> 1,...,9,10,11,...,20
pagination(11, 20) -> 1,...,10,11,12,...,20
pagination(12, 20) -> 1,...,11,12,13,...,20
pagination(13, 20) -> 1,...,12,13,14,...,20
pagination(14, 20) -> 1,...,13,14,15,...,20
pagination(15, 20) -> 1,...,14,15,16,...,20
pagination(16, 20) -> 1,...,15,16,17,...,20
pagination(17, 20) -> 1,...,16,17,18,19,20
pagination(18, 20) -> 1,...,16,17,18,19,20
pagination(19, 20) -> 1,...,16,17,18,19,20
*/

Hello. :)
I'm trying this and the output is not consistent. The ellipsis must not be part of displaySize. If I set displaySize to 7, the output is 1,...,4,5,6,...,20, but it should be 1,...,3,4,5,6,7,...,20. Your solution is very fast, can you fix it, please?