Get the total number of nodes in a tree

treesize.js

// Iterative
const size = (tree) => {
  const axe = [tree];
  let total = 0;

  if(!tree){
    return n;
  }

  while(axe.length) {
    const n = axe.shift();
    total++;

    n.left && axe.push(n.left);
    n.right && axe.push(n.right);
  }

  return total;
}

// Recursive
const size = (tree) => {
  if(!tree){
    return 0;
  }

  return size(tree.left) + 1 + size(tree.right);
}