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

You can't really sync up with the server. Measuring the time your server request needs (as MikeWyatt suggested) is not a good indicator on the latency.

Only your server knows when he responds a request. Therefore, it should send that information back with the answer. With Date.now() - new Date(timestringOfServerResponse) you can measure the latency exactly. Yet I'm not sure why you would need that value.

To sync an app between mulitiple devices, the server should send them which action to perform when. The "when" should not be "as soon as you get my response", but a exact timestamp. As far as the system clocks of your devices are accurate and synced (they usually are), the app will run its methods synchrounously, because it knows what to happen when (or at least: what should have happened then, and it can interpolate what to happen "now").