storing selector in a variable doesn't seem to work

[Gabriel Ciprian Magda]

I am not sure I am doing something wrong, but I try to store the selector name in a variable like this:
$target = $this.closest('.whatever').find('.' + $identifier);
and try to change it like this:
jss.set($target, { borderColor: "#whatever" });
but I get this error:

Uncaught TypeError: t.toLowerCase is not a function

[abdussamad1977]

Variable works fine.
Make sure variable shouldn't have an element, it must have selector text value only.