truncate-names.js

/**
 * Truncate a list of names at return a human friendly sentence fragment.
 * @param {string[]} list A list of name strings to format
 * @param {number} max The maximum number of names to show before appending a count
 * @example
 * // returns "Abi, Jeri and Zoi"
 * truncate(["Abi, Jeri, Zoi"])
 * @example
 * // Returns "Abi and 2 others"
 * truncate(["Abi, Jeri, Zoi"], 1)
 */
function truncate(list, max = 3) {
  // Safety
  max = Math.max(1, max);

  // Short circuit if there's only
  // one item in the array.
  if (list.length === 1) {
    return list;
  }

  let gte = list.length - max;
  let lte = max - list.length;

  let parts = [
    list.slice(0, gte <= lte ? -1 : lte),
    list.length > max ? [gte + " others"] : list.slice(-1)
  ];
  return [parts[0].join(", "), parts[1]].join(" and ");
}