A similar function to jQuery

/**
 * Similar to jQuery function $()
 *
 * https://github.com/alvarotrigo/fullPage.js/blob/master/src/js/common/utils.js#L27
 */
function $(selector, context) {
  context = arguments.length > 1 ? context : document;
  return context ? context.querySelectorAll(selector) : null;
}