Concat list of names in various ways

fuzzyNames.js

let fuzzyNames = {
  _andConcat({ list, last }) {
    return `${list.join(', ')} and ${last.join('')}`;
  },

  _lengthConcat({ list, rest }) {
    let others = rest.length === 1 ? "other" : "others";
    return `${list.join(', ')} and ${rest.length} ${others}`;
  },

  humanize(names, opts={}) {
    if (!names || !Array.isArray(names) || !names.length) {
      throw TypeError(`An array with 1 or more names is expected but received: ${names}`);
    }

    // Don't accidentaly modify original
    let namesCopy = names.concat();

    // Just return it
    if (namesCopy.length === 1) {
      return namesCopy[0];
    }

    // Concat with opts
    if (opts) {
      // Maybe sort
      opts.sort && namesCopy.sort();

      // Maybe length is in range
      if (opts.length > 0 && opts.length < namesCopy.length) {
        return this._lengthConcat({
          list: namesCopy.slice(0, opts.length),
          rest: namesCopy.slice(opts.length)
        });
      }
    }

    // Default concat
    return this._andConcat({
      list: namesCopy.slice(0, namesCopy.length - 1),
      last: namesCopy.slice(namesCopy.length - 1)
    });
  }
};



// TESTS

// ---------------------------------
// Invalid input
// ---------------------------------
fuzzyNames.humanize(); //=> TypeError: An array with 1 or more...
fuzzyNames.humanize([]); //=> TypeError: An array with 1 or more...
fuzzyNames.humanize(null); //=> TypeError: An array with 1 or more...

// ---------------------------------
// Without opts
// ---------------------------------
[
  fuzzyNames.humanize(['Alice']) === "Alice",
  fuzzyNames.humanize(['Alice','Mary']) === "Alice and Mary",
  fuzzyNames.humanize(['Alice','Bob','Mary','Tom','John']) === "Alice, Bob, Mary, Tom and John"
].forEach(console.assert);

// ---------------------------------
// With opts
// ---------------------------------
let names = ['Alice','Bob','Mary','Tom','John'];
[
  fuzzyNames.humanize(names, {}) === "Alice, Bob, Mary, Tom and John",
  fuzzyNames.humanize(names, { length: 0 }) === "Alice, Bob, Mary, Tom and John",
  fuzzyNames.humanize(names, { length: 99 }) === "Alice, Bob, Mary, Tom and John",
  fuzzyNames.humanize(names, { length: -3 }) === "Alice, Bob, Mary, Tom and John",
  fuzzyNames.humanize(names, { length: 1 }) === "Alice and 4 others",
  fuzzyNames.humanize(names, { length: 3 }) === "Alice, Bob, Mary and 2 others",
  fuzzyNames.humanize(names, { length: 4 }) === "Alice, Bob, Mary, Tom and 1 other",
  fuzzyNames.humanize(names, { length: 3, sort: true }) === "Alice, Bob, John and 2 others",
  fuzzyNames.humanize(names, { sort: true }) === "Alice, Bob, John, Mary and Tom"
].forEach(console.assert);