Flatten a folded linked list in node js

Js program for Flatten a folded linked list. Here more information.

/*
  Node JS program for
  Unfold a folded linked list OR
  flatten folded linked list
*/
// Linked list node
class LinkNode
{
	constructor(data)
	{
		this.data = data;
		this.next = null;
	}
}
class SingleLL
{
	constructor()
	{
		this.head = null;
	}
	// Insert node at the beginning of linked list
	addNode(data)
	{
		// Create node
		var node = new LinkNode(data);
		node.next = this.head;
		// Set new head
		this.head = node;
	}
	// Display linked list element
	display()
	{
		if (this.head == null)
		{
			return;
		}
		var temp = this.head;
		// iterating linked list elements
		while (temp != null)
		{
			process.stdout.write(" " + temp.data + " →");
			// Visit to next node
			temp = temp.next;
		}
		console.log(" NULL");
	}
	// This is handle the request of unfold given linked list nodes
	unfoldList()
	{
		if (this.head == null)
		{
			console.log("\n Empty linked list");
			return;
		}
		var temp = this.head;
		var auxiliary = null;
		var hold = null;
		// Loop which is separating the fold elements 
		while (temp.next != null)
		{
			// Get the second element
			hold = temp.next;
			if (hold.next != null)
			{
				// When exists pair of three elements
				temp.next = hold.next;
				// Visit to 3rd element
				temp = hold.next;
			}
			else
			{
				// When get last two elements
				temp.next = null;
			}
			// Add new node at beginning of auxiliary linked list
			hold.next = auxiliary;
			// Make new head node
			auxiliary = hold;
		}
		if (temp != null)
		{
			// Combine lists
			temp.next = auxiliary;
		}
	}
}

function main()
{
	// Create a empty linked lists
	var sll1 = new SingleLL();
	var sll2 = new SingleLL();
	//  Constructed first linked list
	//  2 → 5 → 1 → 8 → 10 → 4 → 9 → 7 → NULL
	sll1.addNode(7);
	sll1.addNode(9);
	sll1.addNode(4);
	sll1.addNode(10);
	sll1.addNode(8);
	sll1.addNode(1);
	sll1.addNode(5);
	sll1.addNode(2);
	// Constructed second linked list
	// 1 → 2 → 3 → 4 → 5 → 6 → 7 → NULL
	sll2.addNode(7);
	sll2.addNode(6);
	sll2.addNode(5);
	sll2.addNode(4);
	sll2.addNode(3);
	sll2.addNode(2);
	sll2.addNode(1);
	// Test A
	console.log(" Before unfold");
	sll1.display();
	sll1.unfoldList();
	console.log(" After unfold");
	sll1.display();
	// Test B
	console.log(" Before unfold");
	sll2.display();
	sll2.unfoldList();
	console.log(" After unfold");
	sll2.display();
}
// Start program execution
main();

Output

 Before unfold
 2 → 5 → 1 → 8 → 10 → 4 → 9 → 7 → NULL
 After unfold
 2 → 1 → 10 → 9 → 7 → 4 → 8 → 5 → NULL
 Before unfold
 1 → 2 → 3 → 4 → 5 → 6 → 7 → NULL
 After unfold
 1 → 3 → 5 → 7 → 6 → 4 → 2 → NULL