[CS-FSLUG] OT: JavaScript: Detecting Item within Viewport

[Timothy Butler]

Hey, everyone,
I posted this just a bit ago over at StackOverflow and thought I'd survey folks on the listserves too:

I would like to fire a function when a user is scrolling and reaches a certain element, so that I can mark that element "read" (think of how posts were marked read after viewing them in the now defunct Google Reader). So, for example, imagine a page like the following:

<div id="1">Node 1</div>
<div id="2">Node 2</div>
<div id="3">Node 3</div>
<div id="4">Node 4</div>
Assuming only the first two <divs> fit within the viewport, I would like to use Dojo's event listener and fire an event when div 3 came into view and again when div 4 came into view. (In addition to my goal of recording when an element has been read, this would also allow me to easily implement infinite scrolling.)

The jQuery Waypoints tool seems to do exactly what I want, but since most of my code uses Dojo, I really don't want to use jQuery just for this one task. I'd like to find a prewritten tool or simple method for doing this that isn't dependent on a library/toolkit other than Dojo (I'm fine with it using Dojo or no library at all).

 It appears Skrollr also does what I am looking for, but only for animation -- that is, it can animate an element based on its relationship to the viewport. This doesn't exactly help, though, since my goal isn't animation but to activate a function (that will make an AJAX call via Dojo) when an element comes within the viewpoint. Suggestions?

Thanks,

Tim



Timothy Butler
tbutler at ofb.biz



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