code: function(jidOrUserId, callback) {
  
          /**
           * Callback for QB.chat.roster.add(). Run without parameters.
           * @callback addRosterCallback
           * */
          var self = this;
          var userJid = this.helpers.jidOrUserId(jidOrUserId);
          var userId = this.helpers.getIdFromNode(userJid).toString();
  
          self.contacts[userId] = {
              subscription: 'none',
              ask: 'subscribe'
          };
  
          self._sendSubscriptionPresence({
              jid: userJid,
              type: 'subscribe'
          });
  
          if (typeof callback === 'function') {
              callback();
          }
      }
docs: Add users to contact list. {@link https://quickblox.com/developers/Web_XMPP_Chat_Sample#Add_users More info.}
  @memberof QB.chat.roster
  @param {String | Number} jidOrUserId - Use opponent id for 1 to 1 chat, and jid for group chat.
  @param {addRosterCallback} callback - The callback function.