Say you want to tack younav bar fixed at the top of the browser’s viewport after a user has scrolled to a certain element in the DOM. In my example this is the menu itself. This snippet checks the vertical position of my main menu and adds a class to it after a visitor has been scrolling that far that it reached the top of the page.
$(document).ready(function() {
var navpos = $('#mainnav').offset();
console.log(navpos.top);
$(window).bind('scroll', function() {
if ($(window).scrollTop() > navpos.top) {
$('#mainnav').addClass('fixed');
}
else {
$('#mainnav').removeClass('fixed');
}
});
});