如何使用 Socket.io 向 node.js 中的特定客户端发送事件/消息？

Question

i'm working on a Node.js app in which we are using socket.io for sending and receiving events/messages to clients. Initially it is sending events to clients using the following statement.

io.sockets.emit('SequenceLoad', data);

But now i want to send events only to specific clients using client specific sockets. I have searched alot regarding this, found some ways but none of them seems to work, found on various SO posts.

Here is the code that i have tried:

const io = require('socket.io')(http);
var socketsCollection = [];
io.on('connection', function (socket) {

  //Saving socket id's for sending events to specific sockets based on their ids
  socketsCollection.push(socket.id);
  socket.on('SequenceLoadServer', function (data) {
     // logger.info('Socket Server | Event: sequenceLoadServer with socket server. \n Data:'+ data);
     console.log("In APP.js for SequenceLoadServer event");
     console.log("Socket Id :" + socket.id);
     var socketId = null;
     setTimeout(function () {
        for (var item of socketsCollection) {
           if(item == socket.id){
              socketId= item;
              break;   
           }
        }
        console.log("Socket after searching Id :" + socketId);
        io.sockets.emit('SequenceLoad', data);   -> This works at the moment

        //Tried the following ways as well but none of them worked 

        //io.sockets.connected[socketId].emit('SequenceLoad', data);
        //io.sockets.socket(socketId).emit('SequenceLoad', data); 
        //io.to(socketId).emit('SequenceLoad', data);
        //io.to('/#' + socketId).emit('SequenceLoad', data);
        //io.to(`${socketId}`).emit('SequenceLoad', data);

     }, 1000 * 3);

  });
}

Version of socket.io in my project:

"socket.io": "^2.2.0",
"socket.io-client": "^2.2.0"

Any help would great, correct me if i'm doing wrong because i'm new to it. Thanks

Answer 1

Given you have the socket instance, you can send to a specific client directly by:

io.to(`${socket.id}`).emit(...);

See Emit cheatsheet

Answer 2

You could keep an object of all sockets connected, where the key is the socket's id and the value can be the socket itself:

let SOCKET_LIST = {};
io.on('connection', function (socket) {
  SOCKET_LIST[socket.id] = socket;
  // more code...
  // retrieving the socket
  selected_socket = SOCKET_LIST[id];
  selected_socket.emit('SequenceLoad', data);

  // Ensure that you delete the socket once it has disconnected:
  socket.on('disconnect', function() {
    delete SOCKET_LIST[socket.id];
  });
}