.then(function(data){ token = data.token; // secondary index key var key = "user_id:" + user_id; redis_client.smembers(key, function(err, members){ if (err) return done(err); // members array should contain token for (var i = 0; i < members.length; i++) { if (members[i] == token) return done(); } done(new Error("user_id secondary index hasn't been used")); }); }).catch(done);