Scheduled image substitution

**RobG** · Jul 23 '05, 04:00 PM

Re: Scheduled image substitution

google@ghosthou nds.com wrote:[color=blue]
> Hello...
>
> I have a website that hosts a java chat room nightly. I'd like to have
> a graphic on the main page that toggles between 2 images - one
> advertising the time of the chat, and another that appears during the
> time the chat is actually in session inviting visitors to the web site
> to join the chat.
>
> Any idea how I might do this in Javascript to schedule the imgage
> substitution using a general meridian time function?
> Thanks for your suggestions!
>[/color]

Presumably the image changes based on the time at the server's
location? Why not just have a script on your server that at a
specified time replaces one image with the other?

You have two source images: a.gif and b.gif. The image in the page is
c.gif. At the specified time for chat to start, your server script
copies a.gif to c.gif. At the next specified time, when chat ends,
b.gif is copied to c.gif, and so /ad infinitum/.

Maybe you need to "touch" the image to update the file creation time so
cached images will update c.gif if you've changed it (but I don't think
so).

Look ma, no JavaScript!

--
Cheers, Rob.

**google@ghosthounds.com** · Jul 23 '05, 04:00 PM

Re: Scheduled image substitution

RobG wrote:[color=blue]
> Why not just have a script on your server that at a
> specified time replaces one image with the other?[/color]

Because I'm even less familiar with server side scripting than I am
with Javascript. ;)
[color=blue]
> You have two source images: a.gif and b.gif. The image in the page[/color]
is[color=blue]
> c.gif. At the specified time for chat to start, your server script
> copies a.gif to c.gif. At the next specified time, when chat ends,
> b.gif is copied to c.gif, and so /ad infinitum/.
>
> Maybe you need to "touch" the image to update the file creation[/color]
time so[color=blue]
> cached images will update c.gif if you've changed it (but I don't[/color]
think[color=blue]
> so).[/color]

Hmmm... that seems extreme overkill for what I'm wanting to do. Maybe
I wasn't clear in my original description, but all I want is a very
basic javascript that, when the page is loaded, displays A.GIF for 22
out of the 24 hours in a day. Except if the page is loaded, between
say UTC 03 and UTC 05 - then it swaps the image with B.GIF

Is a server side script really the better way to do that? I'm not
really concerned that everyone has to see the "Chat now" image at
exactly the same time - I.E. the time on the users PC is fine for the
javascript to get the time from. Unless it can be called from the
server itself in the javascript easily.

Thanks for your input! :)

**Dr John Stockton** · Jul 23 '05, 04:01 PM

Re: Scheduled image substitution

JRS: In article <1102982812.250 323.184910@z14g 2000cwz.googleg roups.com>
, dated Mon, 13 Dec 2004 16:06:52, seen in news:comp.lang. javascript,
google@ghosthou nds.com posted :[color=blue]
>
>I have a website that hosts a java chat room nightly. I'd like to have
>a graphic on the main page that toggles between 2 images - one
>advertising the time of the chat, and another that appears during the
>time the chat is actually in session inviting visitors to the web site
>to join the chat.
>
>Any idea how I might do this in Javascript to schedule the imgage
>substitution using a general meridian time function?
>Thanks for your suggestions![/color]

T = new Date().getUTCHo urs()
src = ['a', 'b'][+(T>=20 && T<22)] + ".gif"

will compute the name of the image to load, changing at 20h & 22h UTC.

new Date()%864e5/36e5|0 // also gets UTC hour-of-day; note |

If you want a Web page to change dynamically when the user's machine
thinks the UTC is right,

new Date()%864e5 // UTC millisecond-of-day

can be used to compute the exact interval to the next status change, for
a setTimeout to load the new image and recompute the interval.

To be more exact, given the potential for user clock adjustment,
calculate the image letter index once a minute and see if it has
changed.

If the times are not whole hours, divide by 6e4 instead to get minute of
UTC day.

BTW, not that it affects you, ISTM that a server cannot initially know
the user's local time, but it may be able to get javascript to send it
the user's offset from GMT.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://www.jibbering.c om/faq/> JL/RC: FAQ of news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> jscr maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.

**google@ghosthounds.com** · Jul 23 '05, 04:01 PM

Re: Scheduled image substitution

RobG wrote:[color=blue]
> Why not just have a script on your server that at a
> specified time replaces one image with the other?[/color]

Because I'm even less familiar with server side scripting than I am
with Javascript. ;)
[color=blue]
> You have two source images: a.gif and b.gif. The image in the page[/color]
is[color=blue]
> c.gif. At the specified time for chat to start, your server script
> copies a.gif to c.gif. At the next specified time, when chat ends,
> b.gif is copied to c.gif, and so /ad infinitum/.
>
> Maybe you need to "touch" the image to update the file creation[/color]
time so[color=blue]
> cached images will update c.gif if you've changed it (but I don't[/color]
think[color=blue]
> so).[/color]

Hmmm... that seems extreme overkill for what I'm wanting to do. Maybe
I wasn't clear in my original description, but all I want is a very
basic javascript that, when the page is loaded, displays A.GIF for 22
out of the 24 hours in a day. Except if the page is loaded, between
say UTC 03 and UTC 05 - then it swaps the image with B.GIF

Is a server side script really the better way to do that? I'm not
really concerned that everyone has to see the "Chat now" image at
exactly the same time - I.E. the time on the users PC is fine for the
javascript to get the time from. Unless it can be called from the
server itself in the javascript easily.

Thanks for your input! :)

**Evertjan.** · Jul 23 '05, 04:01 PM

Re: Scheduled image substitution

wrote on 15 dec 2004 in comp.lang.javas cript:
[color=blue]
> Maybe
> I wasn't clear in my original description, but all I want is a very
> basic javascript that, when the page is loaded, displays A.GIF for 22
> out of the 24 hours in a day. Except if the page is loaded, between
> say UTC 03 and UTC 05 - then it swaps the image with B.GIF
>[/color]

<script type='text/javascript'>
function lookfortime(){
t= new Date()
t= t.getUTCHours()
if(t>2&&t<5)
document.getEle mentById('a').s rc='b.gif'
else
document.getEle mentById('a').s rc='a.gif'

setTimeout('loo kfortime()',600 00)
}
</script>

<body onload='lookfor time()'>
<img src='a.gif' id=a>

NOT TESTED

--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

Scheduled image substitution

Scheduled image substitution

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