Clock on webpage using server and system time?

javascript ajax vb.net clock clock-synchronization
Shawn picture Shawn · Jul 8, 2011 · Viewed 30.8k times · Source

I need to add a clock to a web page. The clock needs to be synchronized with a server but I really don't want to have it constantly check the server as the page will be open 24/7 on several PCs. Is there some way to get the time from the server and then use the systems clock to keep it updated and check the server every 15 minutes or so to keep it synced?

Answer

Jon Egerton picture Jon Egerton · Jul 8, 2011

The way I've gone about this before is:

  • Take the time from the server,
  • Take the time from the client (immediately)
  • Get an offset.
  • When showing the clock, apply the offset to the current time on the client.

You only need to update this occasionally from the server.

The problem that you've got to sort out though is that in making a request to get the time from the server, there will be a lag before you can get the client time. You can probably minimize this by using an ajax request to get the server time and nothing else, thereby cutting overhead and network lag etc.

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