Scroll to Next or Previous <article> element

scroll-next-prev.js

/**document ready**/
$(document).ready(function () {
    /**  scroll to element function **/

    function scrollToElement(selector, time, verticalOffset) {
        time = typeof (time) != 'undefined' ? time : 500;
        verticalOffset = typeof (verticalOffset) != 'undefined' ? verticalOffset : 0;
        element = $(selector);
        offset = element.offset();
        offsetTop = offset.top + verticalOffset;
        $('html, body').animate({
            scrollTop: offsetTop
        }, time);
    }

    count = 0;
    var max_length = $('article').length;
    /* scroll to 150px before article with animation time of 1000ms */
    $('#next').click(function (e) {
        if (count < max_length) {
            count++;
        } else {
            count = 1;    
        }
        e.preventDefault();
        scrollToElement('article:nth-child(' + count + ')', 1000, -150);
    });
      $('#prev').click(function (e) {
        if (count > 1) {
            count--;
        } else {
            count = max_length;        
        }
        e.preventDefault();
        scrollToElement('article:nth-child(' + count + ')', 1000, -150);
    });
});