Function when in viewport

 // Check to see if in viewport
$.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;
};

// if in viewport - Do this
$(window).on('resize scroll', function() {
    if ($('.animate').is(true) && $('.animate').isInViewport()) {
        $('.animate').addClass('in-viewport');
    } else {
        $('.animate').removeClass('in-viewport');
    }
});