Last li in ul

Last li in ul

Hello all. I am beginner in jquery. my code:

<ul class="chooseList">
<li>111</li>
<li>222</li>
<li>333</li>
</ul>

$(document).ready(function(){
//$('.').hide();
$('.chooseList').children().first().slideDown(200);
$('li').on('click',showNextImage);
});

function showNextImage() {
$(this).slideUp(10);
if ($(this) === $('.chooseList li:last')) {
alert('last');
}
else {
$(this).next().slideDown(200);
}
}

I need : when I click on last li to show alert message . What I did wrong?
Thank in advance)