Socket IO makes multiple connections when the page is refreshed - Node JS

Question

I have developed a scrapping tool, that scraps jobs from all websites and save them into the database. I have made my own default log where I get messages(errors, info) etc. I am using socket.io to update my view in real time and for database too.

The problem is when I start the app it perfectly get make socket, and database connections. But when I try to refresh the page, the same connection is made again twice with the same message and different ID's. As much I refresh the page the connections are made, and the id get changed, but for all made connection they use one ID,

Below is the Log which shows it :

I have uploaded this video, please check this as well. Try to watch the very beginning, and then at 01:41 and 03:06, before starting scrapping of the first site the connection is established, but when second website scrapping is started, the Internet Connection message is given twice, and the same stands for when third website scrapping is started, the number of messages get doubled every time. I don't know why.

I have tried following the answer of this question, but still no success. The code is 600+ lines on server file, and 150+ lines second file and same on the client side, that's why I can't upload all and it's a bit confidential.

But the socket connection on the client and server is like this:

Server Side

const express              =    require("express");
const app                  =    express();
const scrap                =    require("./algorithm");
const event = scrap.defEvent;//imported from another file 
const ms_connect = scrap.ms_connect;
const server = app.listen(8000, function(){ console.log('Listening on 8000'); });
const io                   =    require("socket.io").listen(server);
const internetAvailable    =    require("internet-available");
app.use(express.static(__dirname + "/"));


app.get("/scrap",function(req,res){
    res.sendFile(__dirname+"/index.html");//Set the Default Route
    io.on("connection",function(socket){ //On Socket Connection
        socketSameMess("Socket",'Sockets Connection Made on ID : <span style="color:#03a9f4;">'+socket.id+'<span>');
        ms_connect.connect(function(err){//On Connection with Database
            if(err) socketSameMess("database_error",err+" "); // If any error in database connection
            socketSameMess("Database ",'Connected to MYSQL Database Successfully...');
        })
    })
})

function eventSameMess(auth,mess){
    //hits the custom console
    defEvent.emit("hitConsole",{a:auth,m:mess});
}

Client Side

var socket = io.connect('http://localhost:8000');
socket.on('connect',function(){
    if(socket.connected){
        initDocument();
    }
})  

Answer 1

Getting multiple messages

Here are some thumb rules for socketio

1. if you listen to any event once, you'll get the message once in the callback

2. if you listen to any event twice, you'll get the message twice in the callback

3. if you listen to any event nth time, you'll get the message nth in the callback

4. If you're listening to any event on page load, don't forget to listen off that event before you leave the page (if an event is not globally)

   • If you forgot to listen off and if you again re-visit page. you'll start listening to events multiple times. because on page load you're listening to the event. and the previous event is not yet stopped by listen off

5. Don't listen to any event in loop, It may listen to it multiple time and you'll get multiple messages on a single change.

connect socket

const socket = io('http://localhost', {
  transports: ['websocket'], 
  upgrade: false
});

listen and listen off an event

let onMessage = (data) => {
  console.log(data);
}
//listen message
socket.on('message', onMessage);

//stop listening message
socket.off('message', onMessage);    

remove all listeners on disconnect

socket.on('disconnect', () => {
   socket.removeAllListeners();
});

---

Use Firecamp to test/debug SocketIO events visually.

Answer 2

i was having the problem that each client was getting two socket connections. I thought something is wrong with sockets. but the problem was

• FrontEnd -> React
• Created the template using create-react-app
• In index.js file it uses something called React.StrictMode
• This mode renders some of the App.js components two times.
• Just remove that React.StrictMode and try to see if your problem is solved.