isScrolledIntoView.js

function isScrolledIntoView(elem)
{
    var $elem = $(elem);
    var $window = $(window);

    var docViewTop = $window.scrollTop();
    var docViewBottom = docViewTop + $window.height();

    var elemTop = $elem.offset().top;
    var elemBottom = elemTop + $elem.height();

    return ((elemBottom <= docViewBottom) && (elemTop >= docViewTop));
}

Thank you for this!

Question about it.... how can I add a threshold to it so the change doesn't happen immediately after entering or leaving the viewport? For example, if the top of an element is up to 100px outside or the bottom is up to -100px inside the viewport, then trigger the change(s).