getBoundingClientRect.js

function isElementInViewport (el) {
    var rect = el.getBoundingClientRect();
    return (
        rect.top >= 0 &&
        rect.left >= 0 &&
        rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) && /*or $(window).height() */
        rect.right <= (window.innerWidth || document.documentElement.clientWidth) /*or $(window).width() */
    );
}

// JQuery
var isElementInViewport = function(check_dom){
var offsetTop = check_dom.offsetTop;

return offsetTop >= $(window).scrollTop() && offsetTop< ($(window).scrollTop()+$(window).height())
};