Hi JudeOsborn,

Any chance you could please provide a test case, where we can see a before (i.e. with the error) and after (without the error)? Also, could you please rebase this on the dev branch of jQuery Tools, and not the master as you have done here?

Thanks.

Here's a JSFiddle that illustrates the problem:

http://jsfiddle.net/T5uvu/1/

You'll see that the problem only surfaces when setting "circular" to true. If you view the "result" frame's console you'll see the message "Uncaught TypeError: Cannot read property 'top' of null". I don't have a CDN version of my fixed version, but all I'm doing is handling a null position().

If item.position() is null, the else part will throw the same error and so should also be modified to be correct when vertical is false.

Yes, good point. I fixed that and simplified the line of code a tiny bit.

But props should be an object: 0 != {top: 0} or {left: 0}, otherwise the animate call should fail or at least would do nothing.

var dir = vertical ? 'top' : 'left',
    props = {},
    pos = item.position();
props[dir] = pos ? -pos[dir] : 0;

If no animation is done when no position is available return self; would be best.