Send message to client from server using socket.io and node.js

Question

I'm working with socket.io and node.js . i am able to broadcast messages from server to all clients but i am facing problem while sending the message from server to specific clients. i am new to this socket.io and node.js

below is code snipped for clients and serve

server code :

var http = require('http'),
fs = require('fs');

var express = require('express');

var app = http.createServer(function (request, response) {
fs.readFile("client.html", 'utf-8', function (error, data) {

if(error)
    {
            responce.writeHead(404);
            responce.write("File does not exist");
            responce.end();
    }
    else
    {
            response.writeHead(200, {'Content-Type': 'text/html'});
            response.write(data);
            response.end();
    }
 });
}).listen(1337);


var io = require('socket.io').listen(app);


var clients = [ ] ;
var socketsOfClients = {};

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


    socket.on('message_to_server', function(data)
    {


            clients.push(socket.id);

            socket(clients[0]).emit("message_to_client" , { message: data["message"] });

    });
});

~

clients code :

<!DOCTYPE html>
<html>
<head>
    <script src="/socket.io/socket.io.js"></script>
    <script type="text/javascript">
        // our socket.io code goes here

        var socketio = io.connect("127.0.0.1:1337");

        socketio.on("message_to_client", function(data) {
        document.getElementById("chatlog").innerHTML = ("<hr/>" +
        data['message'] + document.getElementById("chatlog").innerHTML);
        });

        function sendMessage() {
        var msg = document.getElementById("message_input").value;
        socketio.emit("message_to_server", { message : msg});
        }
    </script>
</head>
<body>
    <input type="text" id="message_input"/>
    <button onclick="sendMessage()">send</button>
    <div id="chatlog"></div>
</body>
</html>

~

when i am executing ,it is giving error like :

socket(clients[0]).emit("message_to_client" , { message: data["message"] });
    ^

TypeError: object is not a function at Socket.

Nicholas Cloud · Accepted Answer · 2014-10-06 13:55:17Z

I think I understand what you are trying to do. You want to address a message to a particular socket by using its ID.

According to the documentation socket is not a function (http://socket.io/docs/server-api/#socket), so invoking it like socket() is causing your code to fail.

Instead of storing the sockets in an array, let's try storing them in a hash instead:

var clients = {};

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

    // store a reference to this socket in the hash, using
    // its id as the hash key
    clients[socket.id] = socket;

    socket.on('message_to_server', function (data) {
            // look up a client socket by id (this would come from
            // the client, and would need to be communicated to the
            // client in some way, perhaps with a broadcast message
            // sent to every client whenever another client "logged in"
            var destination = clients[data.destinationId];

            // if destination is undefined (falsy) it does not
            // exist in the hash
            if (!destination) {
                    return;
            }

            // send a message to the destination
            destination.emit("message_to_client" , { message: data["message"] });
    });
});

If you only want to send a message to the same socket created during connection, you don't have to store a reference to it in a hash or array, because you have access to it within the closure:

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

    socket.on('message_to_server', function (data) {

            // we have a reference to socket from the closure above ^
            socket.emit("message_to_client" , { message: data["message"] });
    });
});

Awesome. Would you kindly mark my answer as the solution so others might benefit from it as well? Thanks!

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