io.emit vs socket.emit

I'm new to socket.io and have run in to something that seems pretty weird. I don't actually know the difference between socket.emit and io.emit but I can't find an explanation anywhere.

io.on('connection', function(socket){
  io.emit('connected')  // <<<< HERE >> socket.emit('connected');
  socket.on('disconnect', function(){
    io.emit('disconnect')
  });
  socket.on('chat message', function(msg){
    io.emit('chat message', msg);
  });
});

server.listen(3000);

That's my server stuff however when I change the io to socket that message only gets displayed when the user who is connecting connects. io.emit sends the message to all users.

Maybe it's supposed to be like that or maybe its just some horrible hack? Let me know if you need the client side HTML.

标签： javascript node.js sockets socket.io

3条回答

Ridiculous、

2楼-- · 2019-01-30 15:23

That's a good question. Here is a sample code that might answer your question.

server.js code:

// Listener for incoming Socket connections

io.on('connection', function(socket){
  socket.on('send', function(msg){
    console.log('message received/sending: ' + msg);
    io.sockets.emit('new', msg);
  });
});

index.html code

<body>
    <ul id="messages"></ul>
    <form action="">
        <input id="m" autocomplete="off" />
        <button type="submit">Send</button>
    </form>
    <script src="https://code.jquery.com/jquery-1.11.1.js"></script>
    <script src="https://cdn.socket.io/socket.io-1.4.5.js"></script>
    <script>
        var socket = io();
        function send(msg) {
            console.log("emitting: " + msg);
            socket.emit('send', { "message": msg });
        }

        socket.on('new', function (msg) {
            console.log("msg " + msg.message);
            $('#messages').append($('<li>').text(msg.message));
        });

        $(function () {
            $('form').submit(function (e) {
                e.preventDefault();
                send($('#m').val());
                $('#m').val('');
                return false;
            });
        });
    </script>
</body>

In index.html "socket.emit('send', { "message": msg });" this line of code actually sends/emits message to server which is waiting to listen on "socket.on('send', function(msg){" this line of code in server.js. Now "io.sockets.emit('new', msg);" this line from server.js emits that message to all its sockets and is displayed to users using its listener in index.html that is "socket.on('new', function (msg) {".

Simply said Each socket emits its msg to server(io is instance of server) and server in turn emits it to all connected sockets. That is how msg sent by any user is displayed to all users. I hope it helps!

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霸刀☆藐视天下

3楼-- · 2019-01-30 15:30

The io variable represents the group of sockets. The code you have starts on line one with providing a function in the second parameter that gives you a socket variable every time a new connection is made. The socket variable is only for communicating with each individual connection. You may not see it in the code but there will be one socket variable for each connection established

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叛逆

4楼-- · 2019-01-30 15:47

Here's a supplementary documentation for reference.

socket.emit('message', "this is a test"); //sending to sender-client only
socket.broadcast.emit('message', "this is a test"); //sending to all clients except sender
socket.broadcast.to('game').emit('message', 'nice game'); //sending to all clients in 'game' room(channel) except sender
socket.to('game').emit('message', 'enjoy the game'); //sending to sender client, only if they are in 'game' room(channel)
socket.broadcast.to(socketid).emit('message', 'for your eyes only'); //sending to individual socketid
io.emit('message', "this is a test"); //sending to all clients, include sender
io.in('game').emit('message', 'cool game'); //sending to all clients in 'game' room(channel), include sender
io.of('myNamespace').emit('message', 'gg'); //sending to all clients in namespace 'myNamespace', include sender
socket.emit(); //send to all connected clients
socket.broadcast.emit(); //send to all connected clients except the one that sent the message
socket.on(); //event listener, can be called on client to execute on server
io.sockets.socket(); //for emiting to specific clients
io.sockets.emit(); //send to all connected clients (same as socket.emit)
io.sockets.on() ; //initial connection from a client.

Hope this helps!.

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