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Binary Tree Traversal, Count, Total in Javascript 

// Node Class
class Node {
  constructor (val, left=null, right=null) {
    this.val = val;
    this.left = left;
    this.right = right;
  }
}

// Binary Tree
const head = new Node(20, 
  new Node(10, 
  new Node(5, 
  new Node(3, 
  new Node(2, 
  new Node(1)), 
  new Node(4)), 
  new Node(8, 
  new Node(7, 
  new Node(6)), 
  new Node(9))), 
  new Node(15, 
  new Node(13, 
  new Node(11, 
  null, 
  new Node(12)), 
  new Node(14)), 
  new Node(18, 
  new Node(16, 
  null, 
  new Node(17)), 
  new Node(19)))), 
  new Node(30, new Node(25, 
  new Node(23, 
  new Node(22, 
  new Node(21)), 
  new Node(24)), 
  new Node(28, 
  new Node(27, 
  new Node(26)), 
  new Node(29))), 
  new Node(35, 
  new Node(33, 
  new Node(31, 
  null, 
  new Node(32)), 
  new Node(34)), 
  new Node(38, 
  new Node(36, 
  null, 
  new Node(37)), 
  new Node(39, 
  null, 
  new Node(40))))), 
  );

// VIEW
//                                                      20
//                                                     10 30
//                        5 15                           |                          25 35
//          3 8            |           13 18            ||           23 28            |            33 38
//   2 4     |    7 9     ||    11 14    |    16 19    |||    22 24    |    27 29    ||     31 34    |    36 39
//1 n | n n || 6 n | n n ||| n 12 | n n || 17 n | n n |||| 21 n | n n || 26 n | n n |||| n 32 | n n || n 37 | n 40

// In Order Tree Traversal
const inOrder = (node) => {
  if(node.left !== null) {
    inOrder(node.left);
  }
  console.log(node.val);
  if(node.right !== null) {
    inOrder(node.right);
  }
}

// Pre Order Tree Traversal
const preOrder = (node) => {
  console.log(node.val);
  if(node.left !== null) {
    preOrder(node.left);
  }
  if(node.right !== null) {
    preOrder(node.right);
  }
}

// Post Order Tree Traversal
const postOrder = (node) => {
  if(node.left !== null) {
    postOrder(node.left);
  }
  if(node.right !== null) {
    postOrder(node.right);
  }
  console.log(node.val);
}

// Node Count Recursively
const nodeCount = (node) => {
  if(node.left !== null) {
    nodeCount(node.left);
  }
  if(node.right !== null) {
    nodeCount(node.right);
  }
  count++;
}

// Sum of all Nodes Recursively
const totalValue = (node) => {
  if(node.left !== null) {
    totalValue(node.left);
  }
  if(node.right !== null) {
    totalValue(node.right);
  }
  total += node.val;
}

// inOrder(head);
// preOrder(head);
// postOrder(head);

let count = 0;
nodeCount(head)
console.log(count);

let total = 0;
totalValue(head)
console.log(total);
// NOTE
// if the values are continuous between 1/0 and n then the total is simply (n*(n+!))/2
// if the values are continuous between m and n then the total is simply ((n*(n+!))/2) - ((m*(m+!))/2)
Run the code here: https://repl.it/@VinitKhandelwal/everything-binary-tree-javascript

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