$('.left').on('mousewheel', function(e){
var delta = e.originalEvent.wheelDelta;
var current = $('.right').scrollTop();
$('.right').scrollTop(current-delta);
});
var h = $('.slider-body').height();
var hiddenEls = [];
$('.slider-body').find('.slider-item').each(function() {
if ($(this).position().top > h)
hiddenEls.push($(this));
});
alert(hiddenEls.length);