code: function (element, selector) {
      var elementPrototype = window.Element.prototype;
      /* istanbul ignore next : Browser polyfill can't be tested */
      var elementMatches = elementPrototype.matches ||
          elementPrototype.matchesSelector ||
          elementPrototype.mozMatchesSelector ||
          elementPrototype.msMatchesSelector ||
          elementPrototype.webkitMatchesSelector;
      // Cache the function and call it
      return (matchesCssSelector = function (element, selector) {
          return elementMatches.call(element, selector);
      })(element, selector);
  }
docs: Polyfill for element.prototype.matches