ReactとNodeでsocket

% npm i socket.io

server=app.listen(port);varsocket=require('socket.io');io=socket(server);// ①io.on('connection',(socket)=>{// ②constusr=Object.keys(io.sockets.sockets).lengthconsole.log("Hi Server")console.log(usr)socket.on('SEND_MESSAGE',function(data){// ③io.emit('RECEIVE_MESSAGE',data);// ④})});

% sudo yarn add socket.io socket.io-client 

importsocketIOClientfrom'socket.io-client'constsocket=socketIOClient(`${API_URL}`,{transports:['websocket']});socket.on('connection',(socket)=>{console.log("Hi client");console.log(socket);});