Question

I want to add some class for specify element when i’m scrolling my page/window, so i use offset for this but it’s not warking – what is wrong? Much thx for help. This is my code:

$(window).scroll(function() {
    var top_offset = $('body').offset().top;
    if ((top_offset >= 40)) {
        $('nav').addClass('docked_nav');
    }
});

Answer 1

You have already fetched the offest value in the variable top_offset, it contains numeric value now and is not an object.
So either use

if (top_offset>= 40) {
        $('nav').addClass('docked_nav');
    }

Or dont use any variable

if ($('body').offset().top >= 40) {
        $('nav').addClass('docked_nav');
    }

Arun Killu’s answer is also need to be considered