insertAt(data, index) {
  if (!this.head) {
    this.head = new Node(data)
    return;
  }
  if (index === 0) {
    this.head = new Node(data, this.head)
    return;
  }
  const previous = this.getAt(index - 1) || this.getLast()
  const node = new Node(data, previous.next)
  previous.next = node
}