code: function cache(app) {
    if (app.locals.config.cacheDb && 'redis' === app.locals.config.cacheDb.connector) {
      // use redis for cache
      let redis = require("redis").createClient(app.locals.config.cacheDb);
      redis.on("error", function (err) {
        app.error(err);
      });
      // clear existing cache on startup
      redis.del('zlSites', 'themeTrees', 'themesConfig');
  
      return {
        // for getting data
        get: function () {
          if (3 == arguments.length) {
            // hash request
            redis.hget(arguments[0], arguments[1], arguments[2]);
          }
          else if (2 == arguments.length) {
            // key request
            redis.get(arguments[0], arguments[1]);
          }
        },
        // for setting data
        set: function () {
          if (4 == arguments.length) {
            // hash request
            redis.hset(arguments[0], arguments[1], arguments[2], arguments[3]);
          }
          else if (3 == arguments.length) {
            // key request
            redis.set(arguments[0], arguments[1], arguments[2]);
          }
        },
        // for setting volatile data with an expiration date
        setvol: function () {
          if (4 == arguments.length) {
            // key request
            redis.set(arguments[0], arguments[1], () => {
              redis.expire(arguments[0], arguments[2], arguments[3]);
            });
          }
        },
        // for deleting data
        del: function () {
          if (3 == arguments.length) {
            // hash request
            redis.hdel(arguments[0], arguments[1], arguments[2]);
          }
          else if (2 == arguments.length) {
            // key request
            redis.del(arguments[0], arguments[1]);
          }
        }
      }
    }
    else {
      // not using cache
      app.error('No config.cacheDb provided. This may affect performance.');
      let e = function() { arguments[arguments.length-1](); }
      return { get: e, set: e, setvol: e, del: e }
    }
  }
docs: currently only redis cache store is supported