express4でjohnny-fiveを使う

app.js

"use strict";

const express = require('express');
const app = express();
const http = require('http').Server(app);
const io = require('socket.io')(http);
const flash = require('connect-flash');
const bodyParser = require('body-parser');
const methodOverride = require('method-override');
const errorHandler = require('errorhandler');
const config = require('config');
const morgan = require('morgan');

// view setting
app.set('view engine', 'pug');
app.set('views', __dirname + '/views');
app.use(morgan('dev'));
app.use(express.static(__dirname + '/public'));

// POSTでdataを受け取るための記述
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());

app.get('/', function (req, res) {
  console.log('GET /');
  res.render('index', { 
    title: 'コントローラ',
  });
});

// johnny-fiveのコード
const five = require("johnny-five"); // Load the node library that lets us talk JS to the Arduino
const board = new five.Board(); // Connect to the Arduino using that library


board.on("ready", function() { // Once the computer is connected to the Arduino
  let temperature = new five.Thermometer({
    pin: "A0",
    toCelsius: function(raw) {
      var val = ((raw * 5 / 1024) - 0.6) * 100;  // 温度計算
      return Math.round(val * 10) / 10;          // 小数点第2位以下四捨五入
    }
  });
  io.on('connection', (client) => {
    client.on('join', (handshake) => {
      console.log(handshake);
    });
    // Every time a 'temperature' event is sent, listen to it and grab its new values 
    temperature.on("data", () => {
      // console.log(temperature.celsius + "°C");
      client.emit('temperature', temperature.celsius);
    });
  });
})

// 5001番を指定
const port = process.env.PORT || 5001;
http.listen(port);

index.pug

extends layout

block append scripts
  script(src='/js/socket.io.js')
  script(src="/js/temperature.js")

block append style
  link(rel='stylesheet', href='/css/style.css')

block content
  #temperature

temperature.js

$(function(){
  var server = io("http://octopi.local:5001");

  server.on('temperature', (value) => {
    $('#temperature').text(value);
  });
});