ll.js

class Node {
  constructor(data = null, next_node = null) {
    this.data = data;
    this.next_node = next_node;
  }
}

class List {
  constructor() {
    this.head = new Node();
  }

  tail(node = this.head) {
    return (!node.next_node) ? node : this.tail(node.next_node);
  }

  append(data) {
    this.tail().next_node = new Node(data);
  }
  
  preppend(data) {
    const oldList = this.head.next_node;
    this.head.next_node = new Node(data);
    this.tail().next_node = oldList;
  }
  
  count(node = this.head, count = -1) {
    count += 1;
    (!node.next_node) ? count : this.count(node.next_node, count);
  }
  
  reset() {
    this.head.next_node = null;
  }
}

const list = new List();

list.append("ok");
list.preppend("wow");
list.append("omg");
list.preppend("lol");

console.log("LIST", list);
console.log("HEAD", list.head);
console.log("TAIL", list.tail());
console.log("COUNT", list.count());

list.reset();

console.log("RESET - LIST", list);
console.log("RESET - HEAD", list.head);
console.log("RESET - TAIL", list.tail());
console.log("RESET - COUNT", list.count());