critical-leddemo/server.js

const express = require('express')
const app = express()

var ioState = {
    dout: [false],
}

const updateState = data => {
    ioState[data.type] = ioState[data.type].map((x, i) =>
        i == data.pin ? data.value : x
    );
    console.log(ioState);
}

app.use('/', express.static('dist'))

app.get('/api/dout/:pin', function (req, res) {
  res.send(ioState.dout[req.params.pin])
})

const server = app.listen(3000, function () {
  console.log('Example app listening on port 3000!')
})

const io = require('socket.io').listen(server);

io.on('connection', socket => {
    socket.emit('ioState', ioState);
    socket.on('update', data => {
        console.log(data);
        updateState(data);
        io.sockets.emit('ioState', ioState);
    });
});