Determining whether jQuery has not found any element

Question

I\'m using jQuery\'s selectors, especially id selector:

$(\"#elementId\")...

How should I determine whether jQuery has found the element or

Answer 1

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

This is the basic, now do whatever you want.