function each(obj, iterator, context) {
  var i = void 0;

  if (!obj) {
    return;
  }

  if (obj.forEach) {
    obj.forEach(iterator, context);
  } else if (obj.length !== undefined) {
    i = 0;
    while (i < obj.length) {
      iterator.call(context, obj[i], i, obj);
      i++;
    }
  } else {
    for (i in obj) {
      obj.hasOwnProperty(i) && iterator.call(context, obj[i], i, obj);
    }
  }
}
@private
walk objects and arrays
@param {Object} obj
@param {Function} iterator
@param {Object} context