critical-leddemo/server.js

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

const DOUT_LUT = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'];

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

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

var ioState = {
    dout: [false, false, false, false],
    din: [false, false, false, 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/dio/:data', function (req, res) {
    const doutNum = ioState.dout.reduce((total, x, i) => x ? total + Math.pow(2, i) : total, 0);
    const doutChar = DOUT_LUT[doutNum];
    res.send(doutChar);

    const dinChar = req.params.data || '0';
    const dinArray = parseInt(dinChar, 16).toString(2).split('').reverse();
    const din = new Array(4).fill(false).map((x, i) => dinArray[i] != '1').reverse();

    if (ioState.din.toString() != din.toString()) {
        ioState.din = din;
        io.emit('ioState', ioState);
        console.log(din);
    }
})

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