NodeJs. Converting circular structure to json Error

Im want send all connected users data about new connection, but receive error "converting circular structure to JSON" during compilation.

for(var user in squad[_m.data.team].clients){
    if(user == _m.data.client){
      squad[_m.data.team].clients[_m.data.client].send(JSON.stringify({request:0,data:squad[_m.data.team]}));  
    }  
  }

So, I searched for reasons and find that this error formed, when I trying reference object themselfs, but I dont.

via Мишка Картмазов