The clock as it was designed shows the system time as it's set on your visitor's machine.
We received a lot of e-mail asking us if the clock could be altered to
show the time in Sydney (or any other specific global location) regardless of where the
visitor came from. Well it can and here are two versions of it that you can create for
your Web page.
We've provided all the files you need for this project on
this month's (October 98) cover CD-ROM.
To view or use the source code you can use any HTML editor,
text editor and most Web browsers.
These routines work well with client side forms and allow you
to program and test your pages easily without having to resort to server side CGI scripts.
Figure 1d: This simple
adaptation of the clock from February's Web Workshop tutorial will display the time in
Sydney on your visitor's PC.
|A simple Sydney clock
The source code in Source Box 1 creates a clock which will show the local time in Sydney
and which can be adapted to show the local time in any city. The alteration which has been
made to the code from the previous version simply adjusts the visitor's time to Sydney
difference in minutes between the visitor's local time and Greenwich Mean Time (GMT). The
code takes this offset and subtracts it from the visitor's local time and then adds the
GMT offset for Sydney which is +10 hours (+11 hours in summer). If you live in Perth,
Darwin, Adelaide or outside Australia, alter this line of code and set the number of hours
your city is ahead of GMT:
myLocalGMT = 10;
A more complex international clock
The source code in Code Box 2 is more elaborate. It shows the Visitor's
local time as well as the time in two other cities, here Sydney and San Francisco have
This code is quite different to the other clock and you will
notice that three instances of the date object have been created -- one for each date.
function such as setTime when you call it. This, in turn, means that the information at
the address itself will be altered by the function. If you only have one date object you
will get errors if you try to use it for the times in all three cities.
You could share one date object between the local time and
Sydney time because the local time is not sent to a function that will alter it. However,
the variables sydneyTime and sanfranTime must be separate instances of the date object or
you'll get logic errors. We have taken the precaution of making all three times different
instances of the date object. In this example the statements which build up a time string
so it can be later displayed on the Web page have been moved to a separate function called
'buildTimeString. Each time a time string is required this function is called and the
current time is sent to it as a parameter.
Figure 2d: This more
sophisticated example shows the time on this London visitor's computer and the
corresponding time in San Francisco and Sydney.