Socket io Throws error : You are trying to attach socket.io to an express request handler function-CodePudding

I am new in WebSocket's so I am trying to Make an application that uses WebSocket's to Update in Realtime. Here is my code:

const PORT = process.env.PORT || 3000;
const INDEX = "./index.html";

const socketIO = require("socket.io");
const express = require("express");

const app = express();

app.get("/", (req, res) => {
    res.sendFile(INDEX, { root: __dirname });
});
app.listen(PORT, () => {
    console.log("SERVER LISTENING ON PORT http://localhost:3000");
});

const io = socketIO(app);
io.on("connection", (socket) => {
    console.log("Client connected");
    socket.on("disconnect", () => console.log("Client disconnected"));
});

This code throws Error As follows:

Error: You are trying to attach socket.io to an express request handler function. Please pass a http.Server instance.

But when I write the code as follows:

const PORT = process.env.PORT || 3000;
const INDEX = "/index.html";

const socketIO = require("socket.io");
const express = require("express");
const server = express()
    .get("/", (req, res) => res.sendFile(INDEX, { root: __dirname }))
    .use("/static", express.static("static"))
    .listen(PORT, () => console.log(`Listening on ${PORT}`));
const io = socketIO(server);
io.on("connection", (socket) => {
    console.log("Client connected");
    socket.on("disconnect", () => console.log("Client disconnected"));
});

It simply Works.

Please Help me What is happening here.

Thank you in advance!!!

CodePudding user response：

socket.io is expecting an instance returned from the app.listen method (where app is an express instance)

At 1st piece of code , you are passing an express instance which is wrong as I mentioned above

The fix for 1st piece of code , so you can understand it better

const PORT = process.env.PORT || 3000
const INDEX = './index.html'

const socketIO = require('socket.io')
const express = require('express')

const app = express()
const server = app.listen(PORT, () => {
  console.log('SERVER LISTENING ON PORT http://localhost:3000')
})
const io = socketIO(server)

app.get('/', (req, res) => {
  res.sendFile(INDEX, { root: __dirname })
})

io.on('connection', (socket) => {
  console.log('Client connected')
  socket.on('disconnect', () => console.log('Client disconnected'))
})