code: function isModifiedSince(req, res) {
      try {
          if (req.headers['if-unmodified-since']) {
              const jobTime = Date.parse(req.headers['if-unmodified-since']);
              const revInfo = mwUtil.parseETag(res.headers.etag);
              return revInfo && uuid.fromString(revInfo.tid).getDate() >= jobTime;
          }
      } catch (e) {
          // Ignore errors from date parsing
      }
      return false;
  }
docs: Checks whether the content has been modified since the timestamp
  in `if-unmodified-since` header of the request
  @param  {Object} req the request
  @param  {Object} res the response
  @return {boolean}    true if content has beed modified