Animation

by Wosley Bago

JavaScript

$.fn.isOnScreen = function(){

            var win = $(window);

            var viewport = {
                top : win.scrollTop(),
                left : win.scrollLeft()
            };
            viewport.right = viewport.left + win.width();
            viewport.bottom = viewport.top + win.height();

            var bounds = this.offset();
            bounds.right = bounds.left + this.outerWidth();
            bounds.bottom = bounds.top + this.outerHeight();

            return (!(viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top || viewport.top > bounds.bottom));

        };

        $(document).on( 'scroll', function() {
            $('#action-box').removeClass('true');
            $('#action-box').removeClass('false');
            var onscreen = $('#action-box').isOnScreen();
            if ( (onscreen) === true ) {
                if (!$('#action-box').hasClass('true')) {
                    $('#action-box').addClass('true');
                }  
            } else { 
                if (!$('#action-box').hasClass('false')) {
                    $('#action-box').addClass('false');
                }
            }
        });