getSequentialFocusNavigationOrder.js

function getSequentialFocusNavigationOrder(nodeList) {
  var els = Array.prototype.slice.call(nodeList);
  els = els.filter(e => e.tabIndex !== -1);
  els = els.filter(e => !e.disabled);
  els = els.sort(function(left, right) {
    if (left.tabIndex === 0) {
      if (right.tabIndex === 0) {
        return 0;
      }
      return 1;
    }
    if (left.tabIndex === right.tabIndex) {
      return 0;
    }
    if (left.tabIndex > right.tabIndex) {
      return 1;
    }
    return -1;
  });
  return els;
}