Sync JS time between multiple devices

Question

I\'m using the wonderful reveal.js library to create a HTML slideshow. My only problem is that I need it to synchronise across multiple devices.

At the moment I am m

Answer 1

How about a different approach: who cares about time? (You're not going to reliably sync the system clock with JavaScript.)

Instead, use a Node server with socket.io to synchronize when your clients advance the slideshow. Instead of the clients deciding when to advance, the server tells them to.

This approach comes with the added bonus of being able to manually fiddle with the slideshow while it's running. In the example that follows, I've added a Next button that causes all connected clients to immediately advance to the next slide.

app.js

var express = require('express')
    , app = express.createServer()
    , io = require('socket.io').listen(app)
    , doT = require('dot')
    , slide = 0
    , slides = [
        'http://placekitten.com/700/400?image=13',
        'http://placekitten.com/700/400?image=14',
        'http://placekitten.com/700/400?image=15',
        'http://placekitten.com/700/400?image=16',
        'http://placekitten.com/700/400?image=1',
        'http://placekitten.com/700/400?image=2',
        'http://placekitten.com/700/400?image=3',
        'http://placekitten.com/700/400?image=4',
        'http://placekitten.com/700/400?image=5',
        'http://placekitten.com/700/400?image=6',
        'http://placekitten.com/700/400?image=7',
        'http://placekitten.com/700/400?image=8',
        'http://placekitten.com/700/400?image=9',
        'http://placekitten.com/700/400?image=10',
        'http://placekitten.com/700/400?image=11',
        'http://placekitten.com/700/400?image=12',
    ];

app.listen(70); // listen on port 70

app.register('.html', doT); // use doT to render templates
app.set('view options', {layout:false}); // keep it simple
doT.templateSettings.strip=false; // don't strip line endings from template file

app.get('/', function(req, res) {
    res.render('index.html', { slide: slide, slides: slides });
});

app.post('/next', function(req, res) {
    next();
    res.send(204); // No Content
});

setInterval(next, 4000); // advance slides every 4 seconds

function next() {
    if (++slide >= slides.length) slide = 0;
    io.sockets.emit('slide', slide);
}

views/index.html

This file is processed as a doT template.

    

        {{~it.slides :url:i}}
            

        {{~}}
    
    Next >

Copy these two files into a folder, then run

$ npm install express socket.io dot
$ node app.js

and navigate to http://localhost:70 in several different windows, then see the magic.