code: function toMap(keySelector, elementSelector) {
    if (!keySelector) return new Map(this);
  
    elementSelector = typeof elementSelector === 'function' ? elementSelector : i => i;
    let map = new Map();
  
    for (let item of this) {
      let key = keySelector(item);
      let element = elementSelector(item);
      map.set(key, element);
    }
  
    return map;
  }
docs: Creates a map from a sequenece according to a specified key selector function, a comparer, and an element selector function.
  
  @param keySelector A function to extract a key from each element.
  @param elementSelector A transform function to produce a result element value from each element.
  @return A map that contains values from the input sequence.
  keySelector: (item) -> key (Required)
  elementSelector: (item) -> value (Optional)