jQuery assertion support / defensive programming?

Question

Is there any built in support in jQuery for basic assertion checking, primarily of things like \'expected number of returned elements\'.

For instance I may have a simple

Answer 1

You probably want http://docs.jquery.com/Traversing/eq#index:

Reduce the set of matched elements to a single element.

If your selector returns no objects then jQuery simply won't run the chained code as it has no elements to run them on