class ListNode {
  constructor(data) {
    this.data = data
    this.next = null
  }
}

class LinkedList {
  constructor(head = null) {
    this.head = head
  }

  size() {
    let count = 0;
    let node = this.head;
    while (node) {
      count++;
      node = node.next
    }
    return count;
  }

  clear() {
    this.head = null;
  }

  getLast() {
    let lastNode = this.head;
    if (lastNode) {
      while (lastNode.next) {
        lastNode = lastNode.next
      }
    }
    return lastNode
  }

  getFirst() {
    return this.head;
  }
}

let node1 = new ListNode(2)
let node2 = new ListNode(5)
node1.next = node2

let list = new LinkedList(node1)

console.log(list.size()) //returns 2
console.log(list.head.next.data) // 5