socket.io emits multiple times

Question

I have got a very basic example. This question has been asked previously multiple times in stack overflow itself but I could not get the right answer so I am going with this basic example.

Server:

var app    = require('express')();
var server = require('http').Server(app);
var io     = require('socket.io')(server);

server.listen(3000);

app.get('/', function (req, res) {
  res.sendfile(__dirname + '/index.html');
});

io.on('connection', function (socket) {
  socket.on('chat', function (data) {
    var op = false;
    if( data.id == '1234' ){
       op = 'yes';
    }else{
       op = 'no';
    } 
    socket.emit('result', { hello: op });
  });
});

Client:

<html>
    <body>
        <button onclick="check()">Test Me :-)</button>
        <script src="/socket.io/socket.io.js"></script>
        <script>
          var socket = io.connect('http://localhost:3000');

          var check = function(){

            var data = { id : '234'};
            socket.emit('chat', data);

            socket.on('result', function(data){
                console.log('The data is '+data)
            })
          }
        </script>
    </body>
</html>

When I click the test me button for the first time socket.emit('result', { hello: 'world' }); it is emitted one time. And in the console I am getting this printed:

console.log('The data is '+data)

But when I click once again I get this printed thrice:

console.log('The data is '+data)
console.log('The data is '+data)
console.log('The data is '+data)

When I click for the third time I get printed six times:

console.log('The data is '+data)
console.log('The data is '+data)
console.log('The data is '+data)
console.log('The data is '+data)
console.log('The data is '+data)
console.log('The data is '+data)

Like this it is multiplying and going.

Can anyone please give me the insight on how to solve this problem. Your help is greatly appreciated. Thanks!

how did you solve this??? – Pragati Dugar Apr 22 '20 at 21:43 — Pragati Dugar, Apr 22 '20 at 21:43

cesarluis · Accepted Answer · 2015-08-28T08:48:27.457

I think you are adding more and more listeners to 'result' each call you make to check.

First time click -> call 1 console.log from call 1 listener

Second time click -> call 1 console.log from call 1 listener + call 2 console.log from call 1 listener + call 2 console.log from call 2 listener

Third time -> The previous logs + call 3 console.log from call 1 listener + call 3 console.log from call 2 listener and call 3 console.log from call 3 listener.

Try putting the listener for 'result' out of the function:

<html>
 <body>
    <button onclick="check()">Test Me :-)</button>
    <script src="/socket.io/socket.io.js"></script>
    <script>
      var socket = io.connect('http://localhost:3000');

       socket.on('result', function(data){
            console.log('The data is '+data)
        })
      var check = function(){

        var data = { id : '234'};
        socket.emit('chat', data);
      }
    </script>
 </body>
</html>

score 19 · Answer 2 · edited Jan 04 '21 at 20:58

19

For the client side you can use socket.once() instead of socket.on(). Example:

socket.once('result', function(data){
 console.log('The data is '+data)
})

Reference: https://socket.io/docs/v3/listening-to-events/#socket-once-eventName-listener

edited Jan 04 '21 at 20:58

Paolo

17,649
21
81
115

answered Dec 18 '19 at 13:03

Shivam Sagar

209
2
4

this worked for me, thanks – Zionnite Dec 16 '21 at 10:17

Alex · Answer 3 · 2018-10-25T23:58:16.667

I didn't read the question, but I'm putting this on here to help the others, cause I hadn't find this kind of answer yet.

In my case, I was calling the function next multiple times, just like so

io.use(async (socket, next) => {
    let req = socket.request
    let res = req.res || {}

    someMiddleware()(req, res, next)
    anotherMiddleware({extended: false})(req, res, next)
    anotherMiddleware()(req, res, next)
    anotherMiddleware(req, res, next)
    anotherMiddleware()(req, res, next)
    anotherMiddleware()(req, res, next)
})

Every time I was calling a middleware, the next function was getting called and on('connection') was being called too. What I got to do was overwrite the next and put it inside the last middleware, so connection get called just once.

. . .
let originalNext = next
next = () => {} // NOW its not going to annoy anymore
someMiddleware()(req, res, next)
anotherMiddleware({extended: false})(req, res, next)
anotherMiddleware()(req, res, next)
anotherMiddleware(req, res, next)
anotherMiddleware()(req, res, next)
anotherMiddleware()(req, res, originalNext) //next get called <
. . .

I don't understand why you call async func without await inside. — Psartek, Dec 13 '19 at 06:52

socket.io emits multiple times

3 Answers3

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