The logic to insert an element in a circular linked list is the same as to insert an element in a normal linked list. The difference in the circular linked list is that we also need to link the last node's next reference to the head node. The following is the insert method for the CircularLinkedList class:
insert(element, index) { if (index >= 0 && index <= this.count) { const node = new Node(element); let current = this.head; if (index === 0) { if (this.head == null) { this.head = node; // {1} node.next = this.head; // {2} NEW } else { node.next = current; // {3} current = this.getElementAt(this.size()); // {4} // update last element this.head = node; // {5} current.next = this.head; // {6} NEW }