jquery - detect if 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], so the way I do it now is:

alert($('#notAnElement').get(0));

which will write "undefined", and so you can do a check for that. But it seems very bad. What other way is there?

Answer 1

if( $("#anid").length ){
  alert("element(s) found")
}else{
  alert("nothing found")  
}

Answer 2

The selector returns an array of jQuery objects. If no matching elements are found, it returns an empty array. You can check the length or size() of the array returned by the selector or check whether the first array element is 'undefined'.

You can use any the following examples inside an IF statement and they all produce the same result. True, if the selector found a matching element, false otherwise.

$('#notAnElement').length > 0
$('#notAnElement').size() > 0
$('#notAnElement').get(0) !== undefined
$('#notAnElement')[0] !== undefined

Answer 3

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.

Answer 4

This will help you.

http://praveenbattula.blogspot.com/2010/01/how-to-check-jquery-object-is-null.html