ccess to XMLHttpRequest at 'http://localhost:8000/socket.io/?EIO=4&transport=polling&t=NSlavVc' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. code example

Example: socket io with cors

const io = require("socket.io")(httpServer, 
  { 
  cors: {    
    origin: "*",    
    methods: ["GET", "POST"]  
  }});