Check if Item is in viewport -> add class if it is - remove class if it isn't

main.js

(function ($) {
    var digthisAddClassToElement = function (element) {
        //cache the DOM
        //use the element send through function as the dom element
        var $element = $(element);

        //scoped helper functions
        var isInViewport = function (elem) {
            var bounding = elem.getBoundingClientRect();
            return (
                bounding.top >= 0 &&
                bounding.left >= 0 &&
                bounding.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
                bounding.right <= (window.innerWidth || document.documentElement.clientWidth)
            );
        };

        var addRemoveClassFromElement = function () {
            $element.each(function (index, element) {
                var $el = $(element);
                if (isInViewport(element)) {
                    $el.addClass('digthis');
                } else {
                    $el.removeClass('digthis');
                }
            });
        };

        //event listener
        $(window).on('scroll', addRemoveClassFromElement);

        //default action
        addRemoveClassFromElement();
    };

    $(function () {
        digthisAddClassToElement('.item');
    });

})(jQuery)