function test_presence() {
    let state = {};
    const stateFromServer = {};

    const onJoin = (id: string, current: any, newPres: any) => {
      if(!current){
        console.log("user has entered for the first time", newPres)
      } else {
        console.log("user additional presence", newPres)
      }
    };

    const onLeave = (id: string, current: any, leftPres: any) => {
      if(current.metas.length === 0){
        console.log("user has left from all devices", leftPres)
      } else {
        console.log("user left from a device", leftPres)
      }
    };

    state = Presence.syncState(state, stateFromServer, onJoin, onLeave);

    const listBy = (id: string, {metas: [first, ...rest]} : {metas: any[]}) => {
      first.count = rest.length + 1;
      first.id = id;

      return first;
    };

    const onlineUsers = Presence.list(state, listBy);
}

 channel.on('presence_state', (state) => {
   presenceState = Presence.syncState(presenceState, state);
   logState(presenceState);
 });

 const logState = (state: Object) => {
   Presence.list(state, (id: string) => id).forEach(console.log);
 };