construct a linked list from 2d matrix in node js

Js program for construct a linked list from 2d matrix. Here problem description and explanation.

// Node JS program for
// Construct a linked list from 2D matrix
class LinkNode
{
	constructor(data)
	{
		this.data = data;
		this.next = null;
		this.down = null;
	}
}
class DoublyLinkedList
{
	constructor()
	{
		this.head = null;
	}
	display()
	{
		if (this.head == null)
		{
			process.stdout.write("Empty linked list");
		}
		else
		{
			var front = this.head;
			var right = null;
			while (front != null)
			{
				right = front;
				while (right != null)
				{
					process.stdout.write(right.data + "  ");
					right = right.next;
				}
				process.stdout.write("\n");
				// Visit to down node
				front = front.down;
			}
		}
	}
	insertData(matrix, rows, cols)
	{
		// Some auxiliary variables
		var levelHead = null;
		var root = null;
		var perv = null;
		var i = 0;
		var j = 0;
		// Add first row elements into result list 
		while (i < cols)
		{
			if (this.head == null)
			{
				// Add first node
				this.head = new LinkNode(matrix[0][i]);
				levelHead = this.head;
			}
			else
			{
				// next head
				levelHead.next = new LinkNode(matrix[0][i]);
				levelHead = levelHead.next;
			}
			i++;
		}
		// Get first element    
		levelHead = this.head;
		i = 1;
		// Add all the bottom element of each column
		while (i < rows)
		{
			root = null;
			perv = root;
			while (j < cols)
			{
				levelHead.down = new LinkNode(matrix[i][j]);
				if (root == null)
				{
					root = levelHead.down;
					perv = root;
				}
				else
				{
					perv.next = levelHead.down;
					perv = levelHead.down;
				}
				levelHead = levelHead.next;
				j++;
			}
			levelHead = root;
			// reset col
			j = 0;
			// change row
			i++;
		}
	}
}

function main()
{
	var dll = new DoublyLinkedList();
	// Create 2D metrix
	var matrix = [
		[1, 6, 9, 2, -9],
		[2, 5, -5, 7, 1],
		[3, 4, 1, 8, 2]
	];
	var rows = matrix.length;
	var cols = matrix[0].length;
	dll.insertData(matrix, rows, cols);
	dll.display();
}
// Start program execution
main();

Output

1  6  9  2  -9
2  5  -5  7  1
3  4  1  8  2