code: function last(iterable, fn) {
    const iter = iterable[Symbol.iterator]();
    let {done, value} = iter.next();
    if (done)
      return fn();
    while(true) {
      let {done, value: nextvalue} = iter.next();
      if (done)
        return value;
      value = nextvalue;
    } // while
  }
docs: first