The seed value (the second argument to reduce) is the empty string, which doubles as the answer for an empty input array and as the initial "best so far". The strict > comparison means ties go to whichever string came first; flip to >= to prefer the latest. For very large arrays this is O(n) and walks the array once, which beats sorting (O(n log n)) when you only need the single best item. If you need the longest N strings, sort by length and take a slice instead.

map(s => s.length) is the obvious one-liner for a plain length list. The interesting addition is sorting the original strings by length: spread the input first so sort does not mutate the caller's array, then return a length-aware comparator. Defaulting to descending matches the common ask ("show me the longest first") and the optional 'asc' flag covers the inverse without adding a second function. The combined topNLengths helper is a useful pattern for building leaderboards or summary tables: shape and slice once, return the structured records.