Scroll fixed header functions

// menu scroll
var lastScrollTop = 0;
var lastScrollChange = 0;
var scrollDown = true;
var topOffset = 100;
var lastScrollChangeOffset = 100;

$(window).scroll(function(event){
    checkScroll();
});
checkScroll();

function checkScroll(){
    var st = $(this).scrollTop();
    if(st < lastScrollTop){
        if(!scrollDown){
            lastScrollChange = st;
            scrollDown = true;
        }
    }else{
        if(scrollDown){
            lastScrollChange = st;
            scrollDown = false;
        }
    }
    if(st - lastScrollChange > lastScrollChangeOffset){
        lastScrollChange = st;
        if(!scrollDown){
            $("body").addClass("down");
        }else{
            $("body").removeClass("down");
        }
    }
    if(st > topOffset){
        $("body").addClass("scroll");
    }else{
        $("body").removeClass("scroll");
    }
    lastScrollTop = st;
}