longestItem

Takes any number of iterable objects or objects with a length property and returns the longest one.

• Use Array.prototype.reduce(), comparing the length of objects to find the longest one.
• If multiple objects have the same length, the first one will be returned.
• Returns undefined if no arguments are provided.

const longestItem = (...vals) =>
  vals.reduce((a, x) => (x.length > a.length ? x : a));

longestItem('this', 'is', 'a', 'testcase'); // 'testcase'
longestItem(...['a', 'ab', 'abc']); // 'abc'
longestItem(...['a', 'ab', 'abc'], 'abcd'); // 'abcd'
longestItem([1, 2, 3], [1, 2], [1, 2, 3, 4, 5]); // [1, 2, 3, 4, 5]
longestItem([1, 2, 3], 'foobar'); // 'foobar'