whitespace-only selectors throw "Syntax error, unrecognized expression"

[Tomalak]

$(" ") throws a syntax error. $("") does not.

The former case can happen when evaluating a HTML Ajax response, for example. When the the response data is passed to jQuery for evaluation it could happens to be a whitespace only string.

Trimming the string before passing it to jQuery fixes this. But realistically, the two variants should yield the same result - an empty jQuery object.

[john]

Why should it be the same result? The first is an expression (albeit an invalid one) the second is no expression at all. I suspect that you may just want to trim the result in your application.