jQuery error Cannot read property 'top' of undefined`

Question

I need to detect scroll direction on mouseenter on certain div so I try to use code below

$.fn.scroll = function () {
var $this = $(this);
var $list = $(this).find('ul');
var $lis = $list.find('li');
var direction;

$this.addClass('scroll');
$list.addClass('slides-list');
$lis.addClass('slide');
$lis.filter(':first').addClass('current');
$lis.filter(':not(:first)').addClass('past');

$this.on('mouseenter', function(){

    var lastScrollTop = $this.offset().top;

    $(window).scroll(function () {
        if ($this.hasClass('animated')) {
            return;
        }

        var scrollTop = $(window).scrollTop();

        if (scrollTop > lastScrollTop) {
            direction = 'down';
        } else {
            direction = 'up';
        }

        lastScrollTop = scrollTop;
    });

});
}

$(document).ready(function () {
    $('#scroll').scroll();
});

but in line
var lastScrollTop = $this.offset().top;
I get an error
Uncaught TypeError: Cannot read property 'top' of undefined.

I guess I have some problem with scopes, but I don't know how to fix it?

Have you done a `console.log($this)` to see what you're trying to call `.offset()` on? — MDEV, May 25 '15 at 10:59
That'll be why - window isn't an element and therefore doesn't have the `offsetTop` property, maybe you're after `$this.scrollTop()` ? — MDEV, May 25 '15 at 11:04

score 0 · Answer 1 · edited May 23 '17 at 11:58

0

Try with this readonly property:

https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/offsetTop

And check this question as well

offsetTop vs. jQuery.offset().top

edited May 23 '17 at 11:58

Community

1
1

answered May 25 '15 at 11:01

ChesuCR

9,352
5
51
114

score 0 · Answer 2 · edited May 23 '17 at 11:43

0

Try this

$('#scroll').bind('mousewheel', function(event) {
if (event.originalEvent.wheelDelta >= 0) {
    console.log('Scroll up');
}else {
    console.log('Scroll down');
}});

More on How can I determine the direction of a jQuery scroll event?

edited May 23 '17 at 11:43

Community

1
1

answered May 25 '15 at 11:03

Dusan Krstic

663
10
17

score 0 · Answer 3 · answered May 25 '15 at 11:14

0

Try replacing $this with $(this) or $("#scroll") it works

answered May 25 '15 at 11:14

Cijo V J

261
1
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jQuery error Cannot read property 'top' of undefined`

3 Answers3