Script.aculo.us is a wonderful library of Javascript functions for doing lots of buzzword-friendly snazzy effects. A recent schmancy JS trick is the catfish - a small, unintrusive advertisement that pops up at the bottom of the web page and can be closed without affecting the web page. Looking around I didn't see any existing code to do catfish effects with Script.aculo.us so I decided I'd have to fill the gap.

There are four parts to a catfish - the Javascript libraries (Script.aculo.us, which relies upon Prototype), a little bit of HTML structure on your page, some CSS and a single Javascript line. So lets get to it.

To do any of this fancy stuff you need both the Prototype and Script.aculo.us libraries on your site and then load them into the page as follows:

<script src="js/prototype/prototype.js" type="text/javascript"></script>
<script src="js/script.aculo.us/effects.js" type="text/javascript"></script>

Don't forget to change the paths to whatever is correct for your site.

The HTML below needs to be one of the last segments within your HTML, basically it needs to be the last code before the close-BODY tag, so that nothing else throws it off. There's also a link to hide the catfish, you don't want to upset your visitors!

<div id="footer_ad" style="display:none"> <div id="footer_close">[x] <a href="#" onclick="Effect.BlindUp('footer_ad', {duration:1})">close this</a></div>
Catfish is tasty!
</div>

You can put whatever fillings you like in there - nested divs, etc, basically eat your heart out.

The CSS part is pretty straight forward, basically we're setting the div to be locked to the bottom of the web browser window so it slides over the other content - this is a general trick that works great for e.g. shopping cart totals, menus, etc. I used some fairly ugly colors just to make it stand out during testing :-) And for those who don't know, this should either go in your page's CSS file or within a STYLE tag in your page's HEADer.

#footer_ad {
position: fixed;
bottom: 0px;
display: block;
width: 100%;
background-color: #b7948f;
color: #394a8c;
font-size: 24px;
padding: 10px 0 10px 0;
margin: 0;
left: 0;
border-top: 1px solid #9a5261;
}
#footer_close {
float: right;
width; 50px;
display: block;
font-size: 0.6em;
padding: 5px;
text-align: right;
font-size: 0.8em;
}


Last but not least is the Javascript code to make the screen pop up. The best location for this is your body tag's onload attribute, but you could embed it in the page if needed (within a SCRIPT block):

new Effect.BlindDown('footer_ad', {duration:2});

Put that altogether and you too can have some tasty catfish for your site.

There's one last thing, the way the above code works the catfish will keep popping up every time the page is loaded, its left up to an exercise for you on how you'd like to make the close link make the browser remember to hide it. One idea would be to have the onclick event execute a function on the server side to set a session variable that would indicate the visitor no longer wished to see the catfish, then in the presentation code only display the catfish if the visitor doesn't have this variable set; alternatively some Javascript could set a cookie, but I prefer to consolidate all client data in viewer sessions, so there's only one source for all of the relevant data.

Bon appetitè!