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

I like to use presence, inspired from Ruby on Rails:

$.fn.presence = function () {
    return this.length !== 0 && this;
}

Your example becomes:

alert($('#notAnElement').presence() || "No object found");

I find it superior to the proposed $.fn.exists because you can still use boolean operators or if, but the truthy result is more useful. Another example:

$ul = $elem.find('ul').presence() || $('<ul class="foo">').appendTo($elem)
$ul.append('...')

Answer 2

My favourite is to extend jQuery with this tiny convenience:

$.fn.exists = function () {
    return this.length !== 0;
}

Used like:

$("#notAnElement").exists();

More explicit than using length.