jQuery标题滚动，如何抵消？

Question

我正在考虑使用像 https://jsfiddle.net/mariusc23/s6mLJ/31/ 这样的标题滚动，所以当我向下滚动时，标题会缩回，当我向上滚动时，它会重新出现。

HTML：

<header class="nav-down">
    This is your menu.
</header>
<main>
    This is your body.
</main>
<footer>
    This is your footer.
</footer>

CSS：

body {
    padding-top: 40px;
}
header {
    background: #f5b335;
    height: 40px;
    position: fixed;
    top: 0;
    transition: top 0.2s ease-in-out;
    width: 100%;
}
.nav-up {
    top: -40px;
}
main {
   background:url( data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAPklEQVQYV2O8dOnSfwYg0NPTYwTRuAAj0QqxmYBNM1briFaIzRbi3UiRZ75uNgUHGbfvabgfsHqGaIXYPAMAD8wgC/DOrZ4AAAAASUVORK5CYII=
   ) repeat;
    height: 2000px;
}
footer { background: #ddd;}
* { color: transparent}

jQuery:

// Hide Header on on scroll down
var didScroll;
var lastScrollTop = 0;
var delta = 5;
var navbarHeight = $('header').outerHeight();

$(window).scroll(function(event){
    didScroll = true;
});

setInterval(function() {
    if (didScroll) {
        hasScrolled();
        didScroll = false;
    }
}, 250);

function hasScrolled() {
    var st = $(this).scrollTop();

    // Make sure they scroll more than delta
    if(Math.abs(lastScrollTop - st) <= delta)
        return;

    // If they scrolled down and are past the navbar, add class .nav-up.
    // This is necessary so you never see what is "behind" the navbar.
    if (st > lastScrollTop && st > navbarHeight){
        // Scroll Down
        $('header').removeClass('nav-down').addClass('nav-up');
    } else {
        // Scroll Up
        if(st + $(window).height() < $(document).height()) {
            $('header').removeClass('nav-up').addClass('nav-down');
        }
    }

    lastScrollTop = st;
}

这几乎正是我所需要的，除了在我的主页顶部高约 500 像素的图像的问题。我不希望标题在图像上向上滚动，所以当它到达距离页面顶部 500 像素的位置时，我希望它缩回。

我已经玩过代码，但我无法让它做我需要的事情，有什么想法吗？

Answer 1

因此，当您向下滚动时，标题永远不可见。当您向上滚动时，在图像区域的顶部和底部之间看不到标题。

如果您根本不想在前 500 像素处显示标题，请删除 || st < navbarHeight。

 if (st > 500 + navbarHeight || st < navbarHeight) {
   $('header').removeClass('nav-up').addClass('nav-down');
 } else {
   $('header').removeClass('nav-down').addClass('nav-up');
 }

演示

// Hide Header on on scroll down
var didScroll;
var lastScrollTop = 0;
var delta = 5;
var navbarHeight = $('header').outerHeight();

$(window).scroll(function(event) {
  didScroll = true;
});

setInterval(function() {
  if (didScroll) {
    hasScrolled();
    didScroll = false;
  }
}, 250);

function hasScrolled() {
  var st = $(this).scrollTop();

  // Make sure they scroll more than delta
  if (Math.abs(lastScrollTop - st) <= delta)
    return;

  // If they scrolled down and are past the navbar, add class .nav-up.
  // This is necessary so you never see what is "behind" the navbar.
  if (st > lastScrollTop && st > navbarHeight) {
    // Scroll Down
    $('header').removeClass('nav-down').addClass('nav-up');
  } else {
    // Scroll Up 
    if (st > 500 + navbarHeight || st < navbarHeight) {
      $('header').removeClass('nav-up').addClass('nav-down');
    } else {
      $('header').removeClass('nav-down').addClass('nav-up');
    }
  }
  lastScrollTop = st;
}

body {
  padding-top: 40px;
  margin: 0;
}

header {
  background: #f5b335;
  height: 40px;
  position: fixed;
  top: 0;
  transition: top 0.2s ease-in-out;
  width: 100%;
}

.nav-up {
  top: -40px;
}

main {
  background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAPklEQVQYV2O8dOnSfwYg0NPTYwTRuAAj0QqxmYBNM1briFaIzRbi3UiRZ75uNgUHGbfvabgfsHqGaIXYPAMAD8wgC/DOrZ4AAAAASUVORK5CYII=
) repeat;
  height: 2000px;
}

footer {
  background: #ddd;
}

* {
  color: transparent
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<header class="nav-down">
  This is your menu.
</header>
<main>
  <img src="" width="100%" height="500px" style="background-color:#ccc;" /> This is your body.
</main>
<footer>
  This is your footer.
</footer>

Answer 2

也许将st > navbarHeight 与st > 500 交换？