$ ( element exists ) { do something }

FYI: https://coderwall.com/p/un7keg

COPYPASTA OF MY COMMENT:
It may be a good idea to assign the jQuery object to a var, especially if your selector works on a large DOM.

Concider:

var $testDivs = $("#test").find("div");

if ($testDivs.length) {
  //use $testDivs without searching the DOM again
}