socket.io/examples/webpack-build/index.js

import { io } from "socket.io-client";

const socket = io("http://localhost:3000");

socket.on("connect", () => {
  console.log(`connect ${socket.id}`);
});

socket.on("connect_error", (err) => {
  console.log(`connect_error due to ${err.message}`);
});

socket.on("disconnect", (reason) => {
  console.log(`disconnect due to ${reason}`);
});