Depth First search algorithm in JS

depth_first_search.js

class Node {
  
  constructor(val) {
    this.data = val;
    this.left = null;
    this.right = null;
  }

  getChildren() {
    let children = []
    if (this.left) {
      children.push(this.left)
    }
    if (this.right) {
      children.push(this.right)
    }
    return children
  }
}

class BinarySearchTree {

  constructor() {
    this.root = null;
  }

  insertNode(val) {

    var node = new Node(val)

    var currentNode;

    if (!this.root) {
      this.root = node;
    } else {
      currentNode = this.root;
      while (currentNode) {
        if (val < currentNode.data) {
          if (!currentNode.left) {
            currentNode.left = node;
            break;
          } else {
            currentNode = currentNode.left;
          }
        } else if (val > currentNode.data) {
          if (!currentNode.right) {
            currentNode.right = node;
            break;
          } else {
            currentNode = currentNode.right;
          }
        } else {
          console.log('Ignoring this value as the BST supposed to be a tree containing UNIQUE values');
          break;
        }
      }
    }
  }
}

function depthFirstSearch(tree) {
  let nodes = [] // list of nodes

  getNodes(tree.root.getChildren()) // start recursion with no level_index so default is used

  function getNodes(level, level_index = 0) {
    level.forEach(node => { // loop threw nodes in the level
      if (Array.isArray(nodes[level_index])) {
        nodes[level_index].push(node.data) // if node already in this level then add
      } else {
        nodes[level_index] = [node.data] // first node in this level so create array
      }
      // // repeat with this nodes children and descend 1 level
      getNodes(node.getChildren(), level_index + 1)
    });
  }
  return nodes
}

var BST = new BinarySearchTree();

BST.insertNode(8);
BST.insertNode(3);
BST.insertNode(10);
BST.insertNode(1);
BST.insertNode(6);
BST.insertNode(14);
BST.insertNode(4);
BST.insertNode(7);
BST.insertNode(13);

let nodes = depthFirstSearch(BST)

console.log(nodes) // [ [ 3, 10 ], [ 1, 6, 14 ], [ 4, 7, 13 ] ]

// return list of values from nodes on the 3rd level with comma delimiter
console.log(nodes[2].join(",")) // 4,7,13