code: function max(keySelector, comparer) {
    let itComparer = typeof comparer === 'function' ? comparer : util.defaultComparer;
    let itKeySelector = typeof keySelector === 'function' ? keySelector : (i) => i;
  
    let maximum = this.firstOrDefault();
  
    for (let item of this) {
      maximum = itComparer(itKeySelector(item), itKeySelector(maximum)) > 0 ? item : maximum;
    }
  
    return maximum;
  }
docs: Returns the maximum value in a sequence.
  
  @param keySelector A transform function to apply to each element.
  @param comparer A comparer function to check with item is greater.
  @return The maximum value in the sequence.
  keySelector: (T) -> key
  comparer: (item1, item2) -> -1|0|1