querySelectorAll.js

function checkSelector(node, selectors) {
  if (selectors.length === 0) {
    return false;
  }
  var currentSel = selectors.shift();
  if (currentSel === '>') {
    return checkSelector(node, selectors);
  }
  if (currentSel.charAt(0) === '.' && node.classList.contains(currentSel.substr(1))) {
    return true;
  }
  return false;
}

function querySelectorAll(node, selector) {
  var selectors = selectors.replace(/\s+/g, ' ').split(' ');
  var nodeMatches = [];

  RecursiveDFSTraversal(node, function(node, fnArgs) {
    var selectors = fnArgs.selectors.slice();
    var selectorMatched = checkSelector(node, selectors);
    
    if (selectorMatched) {
      if (selectors.length === 0) {
        nodeMatches.push(node);
        // don't expand this subtree
        return false;
      } else {
        return {selectors: selectors};
      }
    }
    // don't expand this subtree
    return false;
  }, 
  {
    selectors: selectors
  });
  return nodeMatches;
}