Find kth smallest element in BST node js

Js program for Find kth smallest element in BST. Here mentioned other language solution.

// Node JS program for
// K’th smallest element in Binary Search Tree
class TreeNode
{
	constructor(data)
	{
		this.data = data;
		this.left = null;
		this.right = null;
	}
}
class BinarySearchTree
{
	constructor()
	{
		this.root = null;
	}
	// Insert a node element
	insert(node, data)
	{
		if (node != null)
		{
			if (node.data >= data)
			{
				// When new element is smaller or equal to current node
				node.left = this.insert(node.left, data);
			}
			else
			{
				// When new element is higher to current node
				node.right = this.insert(node.right, data);
			}
			// Important to manage new node
			return node;
		}
		else
		{
			return new TreeNode(data);
		}
	}
	// Find the kth smallest node in BST
	findKthSmallest(node, k)
	{
		if (node != null)
		{
			// Visit left subtree
			this.findKthSmallest(node.left, k);
			if (this.counter == k)
			{
				// Stop recursion
				return;
			}
			if (this.element == null || this.element.data < node.data)
			{
				// Modified counter variable by one
				this.counter++;
				// Collect possible result
				this.element = node;
			}
			// Visit right subtree
			this.findKthSmallest(node.right, k);
		}
	}
	printKthSsmallest(k)
	{
		if (k <= 0)
		{
			// When given k is not valid positive values
			console.log("Invalid node position " + k);
		}
		else if (this.root == null)
		{
			// When BST are no have elements
			console.log("Empty Binary Search Tree");
		}
		else
		{
			// Reset values
			this.counter = 0;
			this.element = null;
			// Find result
			this.findKthSmallest(this.root, k);
			if (this.counter < k)
			{
				// If In case given kth smallest node are
				// Not exist in binary search tree, then
				console.log("Given " + k + " smallest node are not exist " + this.counter);
			}
			else
			{
				console.log("[" + k + "] smallest node : " + this.element.data);
			}
		}
	}
	// Handle request to add new node
	addNode(key)
	{
		this.root = this.insert(this.root, key);
	}
}

function main()
{
	var tree = new BinarySearchTree();
	/*
	    Make Tree
	    ----------
	        7
	       / \ 
	      /   \
	     4     9
	    / \   / \
	   3   5 8   10
	      /    
	     4     
	*/
	// Add node
	tree.addNode(7);
	tree.addNode(4);
	tree.addNode(3);
	tree.addNode(5);
	tree.addNode(9);
	tree.addNode(8);
	tree.addNode(10);
	tree.addNode(4);
	// Testing
	tree.printKthSsmallest(6);
	tree.printKthSsmallest(4);
	tree.printKthSsmallest(3);
}
// Start program execution
main();

Output

[6] smallest node : 9
[4] smallest node : 7
[3] smallest node : 5