Introduction
ServerDate is used in web pages to make the server's clock available to the client's browser via Javascript.
You can use it when you want to display the current time but don't trust the browser's clock to be accurate, or to synchronize events for different users of your web site by synching them all to the server's clock.
Usage is simple. Add one <SCRIPT>
element to your web page and then you can
use the ServerDate
object in Javascript just like you use the built-in Date
object, except that it reflects the server's time instead of the client's.
Requirements
You need Node.js or PHP running on your web server.
ServerDate has been tested in the following browsers:
- Chrome 23.0.1271.64
- Firefox 16.0.2
- Safari 6.0.1 (7536.26.14)
Installation
Node.js Server
Install with npm:
$ npm install serverdate
Make your server look something like the example in the Node.js
directory and
include the following <SCRIPT>
element in your web page:
<SCRIPT src="ServerDate.js"></SCRIPT>
PHP
Upload ServerDate.js
and ServerDate.php
to your web server and include the
following <SCRIPT>
element in your web page:
<SCRIPT src="ServerDate.php"></SCRIPT>
Usage
You may then use ServerDate
as you would use the Date
object or one of its
instances, e.g.:
> ServerDate()
"Mon Aug 13 2012 20:26:34 GMT-0300 (ART)"
> ServerDate.now()
1344900478753
> ServerDate.getMilliseconds()
22
There is also a new method to get the precision of ServerDate's estimate of the server's clock (in milliseconds):
> ServerDate.toLocaleString() + " ± " + ServerDate.getPrecision() + " ms"
"Tue Aug 14 01:01:49 2012 ± 108 ms"
You can see the difference between the server's clock and the browsers clock, in milliseconds:
> ServerDate - new Date()
39
There is no constructor because it doesn't make sense to create more than one
instance of ServerDate
.
Methods from Date
to change the time, such as setMinutes
, are not defined:
> ServerDate.setMinutes
undefined
ServerDate
is synchronized with the server's clock when it is first loaded and
then re-synchronizes itself from time to time to keep the two clocks from
drifting apart.
See the included file example.html for an example of usage.
Versioning
ServerDate complies with Semantic Versioning.
References
- "Probabilistic clock synchronization" by Flaviu Cristian Cristian, F. (1989), "Probabilistic clock synchronization", Distributed Computing (Springer) 3 (3): 146–158, DOI:10.1007/BF01784024
- MikeWyatt's answer and Willem Mulder's comment in Sync JS time between multiple devices
- Rob W's answer to How to synchronise a client webpage timer with the server
Copyright
Copyright 2012 David Braun
This file is part of ServerDate.
ServerDate is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
ServerDate is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License along with ServerDate. If not, see http://www.gnu.org/licenses/.