code: function querySelectorAll (query, context) {
    return Array.prototype.slice.call(
      (context || document).querySelectorAll(query)
    )
  }
docs: querySelectorAll : querySelectorAll(query, [element])
  Convenience function to access `document.querySelectorAll`. Unlike the
  default version, this always returns an array.
  
  If a 2nd parameter `element` is given, it only searches for descendants of
  that element.
  
  var each = require('dom101/each');
  var qsa = require('dom101/query-selector-all');
  
  qsa('.button').each(el => {
  addClass('el', 'selected');
  };