Depth and Breath first transversals without recursion in the DOM tree

DOM-dsf-bfs.js

function dfs(root, fn) {
 if (!(root instanceof HTMLElement)) {
  throw new Error('`root` should be an HTML Element');
  return;
 }
 if (!(fn instanceof Function)) {
  fn = function(element) {
   console.debug(element);
  } 
 }
 // Each stack frame contains the parent node to transverse
 var stack = [];
 var current = root;

 while (current !== null || stack.length !== 0) {
  if (current === null) {
   var top = stack[stack.length - 1];
   
   if (top.nextElementSibling !== null) {
    stack.pop();
    stack.push(top.nextElementSibling);
    current = top.nextElementSibling;
   } else {
    stack.pop();
   }
    // visit top
    fn(top);
  } else {
   current = current.firstElementChild;
   if (current !== null) {
    stack.push(current);
   }
  }
 }
 // visit root
 fn(root);
}

function bfs(root, fn) {
 if (!(root instanceof HTMLElement)) {
  throw new Error('`root` should be an HTML Element');
  return;
 }
 if (!(fn instanceof Function)) {
  fn = function(element) {
   console.debug(element);
  } 
 }
 
 var queue = [root];
 
 while (queue.length !== 0) {
  var current = queue.shift();
  // visit current
  fn(current);

  for (var i = 0; i < current.children.length; i++) {
   queue.push(current.children[i]);
  }
 }
}