How can I detect if a selector returns null?

Question

What is the best way to detect if a jQuery-selector returns an empty object. If you do:

alert($(\'#notAnElement\'));

you get [object Object

Answer 1

My preference, and I have no idea why this isn't already in jQuery:

$.fn.orElse = function(elseFunction) {
  if (!this.length) {
    elseFunction();
  }
};

Used like this:

$('#notAnElement').each(function () {
  alert("Wrong, it is an element")
}).orElse(function() {
  alert("Yup, it's not an element")
});

Or, as it looks in CoffeeScript:

$('#notAnElement').each ->
  alert "Wrong, it is an element"; return
.orElse ->
  alert "Yup, it's not an element"