jQuery(document).ready(function(){
    var isInViewport = function(elem) {
        var distance = elem.getBoundingClientRect();
        return (
            distance.top >= 0 &&
            distance.left >= 0 &&
            distance.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
            distance.right <= (window.innerWidth || document.documentElement.clientWidth)
        );
    };
    
    var targetClass = document.querySelector('.thumbs-up');
    var isTargetVisible = false;
    
    window.addEventListener('scroll', function(event) {
            if (isInViewport(targetClass)) {
                if(!isTargetVisible){
                    console.log('thumbs up visible');
                    jQuery('.thumbs-up').addClass("bobbing-thumbs-up");
                    isTargetVisible = true;
                }
            } else {
                if(isTargetVisible){
                    console.log('thumbs up NOT visible');
                    jQuery('.thumbs-up').removeClass("bobbing-thumbs-up");
                    isTargetVisible = false;
                }
            }
    }, false);
});