var currentSection = 0;
var totalSections = document.querySelectorAll("section").length;
$(document).on('click', '.cd-go', function(event){
    event.preventDefault();
    var viewportHeight = $(window).height();
    currentSection++;
    if (currentSection > totalSections - 1) currentSection = totalSections - 1;
    $('html, body').animate({
        scrollTop: viewportHeight * currentSection
    }, 500);
});

var currentSection =    1;
var nextSection = 0

$(document).on('click', '.cd-go', function(event){
        var sec = 1;
    event.preventDefault();
    $("section").each(function(){
        if($(this).inView()){
        currentSection = sec;
        console.log('currentSection =',currentSection);
      }else{
      sec++
      }
        });
    nextSection = currentSection+1;

    var os = $('#section'+nextSection).offset();

    $('html, body').animate({
    scrollTop: os.top,
    scrollLeft: os.left
});
});

$.fn.inView = 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;
};