function BinaryTree() { var Node = function(key) { this.key = key; this.left = null; this.right = null; } var root = null; var insertNode = function(node, newNode) { if (newNode.key < node.key){ if(node.left === null) { node.left = newNode; } else { insertNode(node.left, newNode); } } else { if (node.right === null) { node.right = newNode; } else { insertNode(node.right, newNode); } } } this.insert = function(key) { var newNode = new Node(key); if(root === null){ root = newNode; } else { insertNode(root, newNode) } } this.inOrderTraverseNode = function(node,callback){ if(node !==null) { inOrderTraverseNode(node.left,callback); callback(node.key); inOrderTraverseNode(node.right,callback) } } this.inOrderTraverse = function(callback) { inOrderTraverseNode(root,callback) } } var nodes = [8,3,10,1,6,14,4,7,13]; var binaryTree = new BinaryTree(); nodes.forEach(function(key){ binaryTree.insert(key); }); var callback = function(key) { console.log(key) } binaryTree.inOrderTraverse(callback);