Check if element in viewport and do something

ifInViewport.js

$.fn.isInViewport = function() {
    var elementTop = $(this).offset().top;
    var elementBottom = elementTop + $(this).outerHeight();

    var viewportTop = $(window).scrollTop();
    var viewportBottom = viewportTop + $(window).height();

    return elementBottom > viewportTop && elementTop < viewportBottom && elementBottom < viewportBottom && elementTop > viewportTop;
//     return elementBottom > viewportTop && elementTop < viewportBottom;  
};

$(window).on('resize scroll', function() {
    $('.element').each(function() {
        if ($(this).isInViewport()) {
            $(this).find($('.item')).addClass('active');
        } else {
            $(this).find($('.item')).removeClass('active');
        }
    });
});