jQuery.fn.isInViewport = function() {
var elementTop = jQuery(this).offset().top;
var elementBottom = elementTop + jQuery(this).outerHeight();
var viewportTop = jQuery(window).scrollTop();
var viewportBottom = viewportTop + jQuery(window).height();
return elementBottom > viewportTop && elementTop top_of_element) && (top_of_screen top_of_element) && (top_of_screen < bottom_of_element)){
jQuery(this).addClass("td-in-viewport");
} else {
jQuery(this).removeClass("td-in-viewport");
}
});
});