code: function hincrby(key, field, amount, req) {
    var map = this.getKey(key, req)
      , val;
    if(!map) {
      map = new HashMap();
      this.setKey(key, map, undefined, undefined, undefined, req);
    }
    val = utils.strtoint(map.getKey(field));
    amount = utils.strtoint(amount);
    val += amount;
    map.setKey(field, val);
    return val;
  }
docs: Increments the number stored at field in the
  hash stored at key by increment.