I am making a ticker similar to
the "From
the AP" one at
The Huffington Post, using jQuery.
The ticker rotates through a ul, either by user command (clicking an arrow) or by an auto-scroll.
Each list-item is display:none by default. It is revealed by
the addition of a "showHeadline" class which is display:list-item. HTML for
the UL Looks like this:
<ul class="news" id="news">
<li class="tickerTitle showHeadline">Test Entry</li>
<li class="tickerTitle">Test Entry2</li>
<li class="tickerTitle">Test Entry3</li>
</ul>
When
the user clicks
the right arrow, or
the auto-scroll setTimeout goes
off, it runs a tickForward() function:
function tickForward(){
var $active = $('#news li.showHeadline');
var $next = $active.next();
if($next.length==0) $next = $('#news li:first');
$active.stop(true, true);
$active.fadeOut('slow', function() {$active.removeClass('showHeadline');});
setTimeout(function(){$next.fadeIn('slow', function(){$next.addClass('showHeadline');})}, 1000);
if(isPaused == true){
}
else{
startScroll()
}
};
This is heavily inspired by Jon Raasch's A Simple jQuery Slideshow.
Basically, find what's visible, what should be visible next, make
the visible thing fade and remove
the class that marks it as visible, then fade in
the next thing and add
the class that makes it visible.
Now, everything is hunky-dory if
the auto-scroll is running, kicking
off tickForward() once every three seconds. But if
the user clicks
the arrow button repeatedly, it creates two negative conditions:
Rather than advance quickly through
the list for just
the number of clicks made, it continues scrolling at a faster-than-normal rate indefinitely.
It can produce a situation where two (or more) list items are given
the .showHeadline class, so there's overlap on
the list.
I can see these happening (especially #2) because
the tickForward() function can run concurrently with itself, producing different sets of $active and $next.
So I think my question is:
What would be
the best way to prevent concurrent execution of
the tickForward() method?
Some things I have tried or considered:
Setting a Flag: When tickForward() runs, it sets an isRunning flag to true, and sets it back to false right before it ends.
The logic for
the event handler is set to only call tickForward() if isRunning is false. I tried a simple implementation of this, and isRunning never appeared to be changed.
The jQuery queue(): I think it would be useful to queue up
the tickForward() commands, so if you clicked it five times quickly, it would still run as commanded but wouldn't run concurrently. However, in my cursory reading on
the subject, it appears that a queue has to be attached to
the object its queue applies to, and since my tickForward() method affects multiple lis, I don't know where I'd attach it.
