haw can i get a variable out of socket.on

Because i want to return it in the function getdata() by :

responseObj.json(resp_);

My issues is that i can't get the variable resp_ from the socket.on !!

This is my code :

function getData(responseObj) {

// ..more code..

io.sockets.on('connection', function (socket) { 
    io.emit('resp',response);
});

   io.sockets.on('connection', function (socket) {                 
         socket.on('resp_',function(resp_){
             socket.on('IOTdata_', function(IOTdata_){

             resp_.categories.push({"label": IOTdata_.date});

        //   resp_.dataset[0].data.push({"value" : IOTdata_.temperature});
        //   resp_.dataset[1].data.push({"value" : IOTdata_.humidity}); 
        //  console.log(resp_);            


           });

      });       
   });  

 responseObj.json(resp_);

}); }

via Hassen Dakhlaoui