Question

I always wondered why jQuery returns true if I’m trying to find elements by id selector that doesnt exist in the DOM structure.

Like this:

<div id="one">one</div>

<script>
    console.log( !!$('#one') ) // prints true
    console.log( !!$('#two') ) // is also true! (empty jQuery object)
    console.log( !!document.getElementById('two') ) // prints false
</script>

I know I can use !!$('#two').length since length === 0 if the object is empty, but it seems logical to me that a selector would return the element if found, otherwise null (like the native document.getElementById does).

F.ex, this logic can’t be done in jQuery:

var div = $('#two') || $('<div id="two"></div>');

Wouldnt it be more logical if the ID selector returned null if not found?

anyone?

Answer 1

This behaviour was chosen because otherwise jQuery would regularly throw NullReference Exceptions

Almost all jQuery functions return a jQuery object as a wrapper around the Dom elements in question, so you can use dot notation.

$("#balloon").css({"color":"red"});

Now imagine $("#balloon") returned null. That means that $("#balloon").css({"color":"red"});
would throw an error, rather than silently doing nothing as you would expect.

Hence, you just gotta use .length or .size().