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

I'm extensively using the COMET pattern here for my real time web application.

To use that in your case you'd need the clients to open an AJAX request to the server and wait for an answer. As soon as it comes the client has to change slides.

On the server you have to hold back all answers till it's time to change slides. (You could be more advanced and delay afterwards on the client for the same time each, but that's most likely not necessary). I can't show you sample code for that here as I don't know what's available to you.

So you are effectively creating an orchestra where the server plays the conductor and all clients are listening to him.

Timing is then determined by the ability of the server to answer the requests at (nearly) the same time plus the network latency.
Usually the clients should be in the same part of the network so latency might be very similar - and the absolute value doesn't hurt here, only the variation.

And there might also be an additional trick helping: don't change the slides with a hard replacement, blend them. This will blur the change so that the eye can't catch the little timing differences that you'll always have.

(If you can't have the server playing conductor you're likely to have to use the solution by MikeWyatt - probably with a few requests and averaging the result, depending on the network setup. In a LAN one request might be enough, going over the full internet a bit over averaging won't hurt...)