Collects all the IDs and classes from a given element down (like document.body)

gistfile1.js

function scan(parent) {
  var found =  {classes: {}, ids: []};
  var unexamined = [parent];
  while (unexamined.length > 0) {
    parent = unexamined.pop();
    var nodeLength = parent.childNodes.length;
    for(var i = 0; i < nodeLength; ++i) {
      node = parent.childNodes[i];
      if (node.nodeType != 1) { continue; }

      unexamined.push(node);
      if (node.id !== '') { found.ids.push(node.id); }

      var classes = node.getAttribute('class');
      if (classes === null) { continue; }
      var parts = classes.split(' ');
      var length = parts.length;
      for(var j = 0; j < length; ++j) {
        var part = parts[j];
        if (part === '') { continue; }
        if (found.classes[part] === undefined) { found.classes[part] = 0; }
        found.classes[part] += 1;
      }
    }
  }
  return found;
}
console.log(scan(document.body));