code: function uuid() {
      var d = Date.now();
      // Use high perf timer if avail.
      /* istanbul ignore next */
      if (typeof performance !== 'undefined' && is_1.isFunction(performance.now))
          d += performance.now();
      return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function (c) {
          var r = (d + Math.random() * 16) % 16 | 0;
          d = Math.floor(d / 16);
          return (c === 'x' ? r : (r & 0x3 | 0x8)).toString(16);
      });
  }
docs: UUID
  Generates a UUID.