return the kth to last node in a linked list

kthToLastNode.ts

function returnKthToLast(head: Node, k: number): Node | null {
  let delta = 0
  let node = head
  
  while (delta < k) {
    node = node.next
    ++delta
    if (!node) {
      return null
    }
  }

  let kthNode = node
  while (true) {
    if (node.next) {
      node = node.next
      kthNode = kthNode.next
    } else {
      return kthNode
    }
  }
}

class Node {
  public next:any 
  public data: number

  constructor(num: number) {
    this.data = num
  }

  public appendToTail = (num: number) => {
    const newNode = new Node(num)
    let node = this
    while (node.next != null) {
      node = node.next
    }
    node.next = newNode
  }
}