traversal.js

const node = val => {
  return {
    data: val,
    left: null,
    right: null
  };
}

const buildTree = () => {
  const root = node(10);
  root.left = node(11);
  root.left.left = node(7);
  root.right = node(9);
  root.right.left = node(15);
  root.right.right = node(8);

  return root;
}

const preOrder = node => {
  if(!node) {
    return;
  }

  console.log(node.data);
  preOrder(node.left);
  preOrder(node.right);
}

const inOrder = node => {
  if(!node) {
    return;
  }

  inOrder(node.left);
  console.log(node.data);
  inOrder(node.right);
}

const postOrder = node => {
  if(!node) {
    return;
  }

  postOrder(node.left);
  postOrder(node.right);
  console.log(node.data);
}

const tree = buildTree();

console.log('Preorder')
preOrder(tree);

console.log('Inorder');
inOrder(tree);

console.log('PostOrder')
postOrder(tree)