Method unshift

src/utils.ts:727–736

Insert at front of list

(value: T)

  /** Insert at front of list */
  unshift(value: T) {
    this.count += 1;
    const newNode: ListNode<T> = {
      next: this.head.next as ListNode<T>,
      prev: this.head as HeadNode<T>,
      value
    };
    this.head.next.prev = newNode;
    this.head.next = newNode;
  }

  private remove(node: ListNode<T> | EmptyNode): T | null {
    if (node === this.head || this.length === 0) {