client.js

$(function(){
var host = "ws://localhost:8888/";
var socket = new WebSocket(host);

socket.onmessage = function(message){
    console.log(socket.readyState + " " + message.data);
}

$("#sendBtn").on("click",function(){
    message = $("#message").val()
    socket.send(message);
});
})

server.js

var ws = require("websocket.io");
var server = ws.listen(8888, => console.log("ws start"));

server.on("connection", function(socket) {
    socket.on("message", function(data) {
        server.clients.forEach((client) => client.send(data));
    });
});