How to emit events in loop using socket.io and node.js? #4713

user-redans · 2023-05-11T12:56:46Z

user-redans
May 11, 2023

I want to emit 5 events message, in a loop, using socket.io and node.js.

This is what I've tried so far:

HTML client:

//client
<!doctype html>
<html>
  <head>
    <title>Socket.IO DEMO - LOOP EMIT Events</title>
    <style>
    </style>
  </head>
  <body>
    <script src="https://cdn.socket.io/4.5.4/socket.io.min.js"></script>
    <script type="text/javascript" src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
    <script>
      var socket = io();
      var global_var = "";

      $(function () {
         //5 loops
          for( let i = 1; i <= 5; i++ ){
            manageEvents_v1(i)
              .then(message => {    
                console.log("call manageEvents_v1() - Promise resolved successfully - message: " + message);   
                //put received data in global variable 'global_var'
                global_var = message;
              })
              .catch(function() {
                console.log("call manageEvents_v1() - Promise is rejected");            
              });

              //use 'global_var' here, every loop, outside callback
            
          }
      });
      
      var manageEvents_v1 = function(data) {
        return new Promise(function(resolve, reject) {
          let timer;

          socket.emit('trigger', data);
      
          function response(message) {
            resolve(message);
            clearTimeout(timer);
            socket.removeListener('feedBack_trigger', response);
          }

          socket.on('feedback_trigger', response); 

          timer = setTimeout(() => {
            reject(new Error("timeout err!"));
            socket.removeListener('feedBack_trigger', response);
          }, 10000);
      
        });
      }

    </script>
  </body>
</html>

Node.JS server:

//server
//////////////////
const express = require('express');
const app = express();
const http = require('http');
const server = http.createServer(app);
const io = require('socket.io')(server);
const session = require("express-session");
const bodyParser = require("body-parser");
const passport = require("passport");
const LocalStrategy = require("passport-local").Strategy;

var port = process.env.PORT || 9090;

const sessionMiddleware = session({ secret: "changeit", resave: false, saveUninitialized: false });
app.use(sessionMiddleware);

app.use(bodyParser.urlencoded({ extended: true }));
app.use(passport.initialize());
app.use(passport.session());

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

const wrap = middleware => (socket, next) => middleware(socket.request, {}, next);
io.use(wrap(sessionMiddleware));
io.use(wrap(passport.initialize())); 
io.use(wrap(passport.session()));


io.sockets.on('connection', function(socket){
  var socketId = socket.id;
    var clientIp = socket.request.connection.remoteAddress;

  console.log("DEBUG - A user connected!");
    console.log("DEBUG - clientIp: " + clientIp + " || socketId: " + socketId);

  socket.on('trigger', function (data) {  
    console.log("\n ----------  BEGIN::EVENT -> trigger  -------------------- \n");
    console.log("DEBUG -> Data RECEIVED from CLIENT: " + data);
    console.log("DEBUG -> SEND back data to CLIENT: " + data);
    socket.emit('feedback_trigger', "hello from server - this is your data: " + data); // Send data to client
  });
});

////////// server listen //////////////////////////////////////////////////
server.listen(port, () => {
  console.log(`listening on *:${port}`);
});

On server console, I've got follow debug messages:

 ----------  BEGIN::EVENT -> trigger  --------------------

DEBUG -> Data RECEIVED from CLIENT: 1
DEBUG -> SEND back data to CLIENT: 1

 ----------  BEGIN::EVENT -> trigger  --------------------

DEBUG -> Data RECEIVED from CLIENT: 2
DEBUG -> SEND back data to CLIENT: 2

 ----------  BEGIN::EVENT -> trigger  --------------------

DEBUG -> Data RECEIVED from CLIENT: 3
DEBUG -> SEND back data to CLIENT: 3

 ----------  BEGIN::EVENT -> trigger  --------------------

DEBUG -> Data RECEIVED from CLIENT: 4
DEBUG -> SEND back data to CLIENT: 4

 ----------  BEGIN::EVENT -> trigger  --------------------

DEBUG -> Data RECEIVED from CLIENT: 5
DEBUG -> SEND back data to CLIENT: 5

As you can see, server messages are good, but on client side, I've received something like that:

I don't know why, but all 5 responses are with first value '1'...I can't received all values from 1 to 5.

I expected from server something like this, after every emit event from server to see a message with right value and at the end in browser console, after all 5 loops are over, to display:

call manageEvents_v1() - Promise resolved successfully - message: hello from server - this is your data: 1
call manageEvents_v1() - Promise resolved successfully - message: hello from server - this is your data: 2
call manageEvents_v1() - Promise resolved successfully - message: hello from server - this is your data: 3
call manageEvents_v1() - Promise resolved successfully - message: hello from server - this is your data: 4
call manageEvents_v1() - Promise resolved successfully - message: hello from server - this is your data: 5

After that I need those values outside Promise callback to assign them to another global variable (global_var)

darrachequesne · 2023-05-15T12:30:12Z

darrachequesne
May 15, 2023
Maintainer

Hi! You are registering 5 distinct listeners for the feedback_trigger event:

var manageEvents_v1 = function(data) {
  // ...
  // called 5 times
  socket.on('feedback_trigger', response);
}

You should use the built-in emitWithAck() method (added in version 4.6.0) instead:

const response = await socket.timeout(10000).emitWithAck('trigger', data);

Reference: https://socket.io/docs/v4/client-api/#socketemitwithackeventname-args

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darrachequesne May 15, 2023 Maintainer

user-redans
May 11, 2023

darrachequesne
May 15, 2023
Maintainer