javascript - anchor 滚动功能干扰滚动事件监听器逻辑以隐藏/显示 "back to top"按钮

Question

我使用 this method 构建了一个滚动到顶部按钮上this page .

我还编写了一个函数，它可以根据 anchor 链接处理滚动到各部分的操作，以便各部分可以平滑地滚动到视口(viewport)中，同时考虑到导航在顶部占用的空间。

这是重现该问题的代码片段:

const navHeight = 42;
const $scrollTopBtn = $('#scroll-top-btn');

$(window).scroll(function() {
  const scrollTop = $(document).scrollTop();

  if (scrollTop > navHeight) {
    $scrollTopBtn.fadeIn();
  } else {
    $scrollTopBtn.fadeOut();
  }
});

$(document).ready(() => {
  $('a[href*="#"]').on('click', function(event) {
    const hash = this.hash;
    
    if (this.hash) {
      event.preventDefault();

      $('html, body').animate({
        scrollTop: $(hash).offset().top - navHeight,
      }, 350);

      window.location.hash = this.hash;
    }
  });
});

body {
  margin: 0;
  font-family: monospace;
}

nav {
  position: sticky;
  top: 0;
  display: flex;
  background: white;
  border-bottom: 2px solid black;
}

a {
  height: 40px;
  display: flex; 
  align-items: center; 
  padding: 0 8px;
  border-right: 2px solid black;
}

.block {
  min-height: 100vh;
  border-bottom: 2px solid black;
  display: flex; 
  justify-content: center;
  padding: 32px 50vw 32px 32px;
  box-sizing: border-box;
}

#scroll-top-btn {
  position: fixed;
  right: 8px;
  bottom: 8px;
  width: 40px;
  height: 40px;
  border: 2px solid black;
  display: flex; 
  align-items: center;
  justify-content: center;
  padding: 0;
  background: white;
}

<nav>
  <a href="#block1">Block 1</a>
  <a href="#block2">Block 2</a>
  <a href="#block3">Block 3</a>
</nav>

<div id="block1" class="block">
  Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</div>

<div id="block2" class="block">
  Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem. Ut enim ad minima veniam, quis nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut aliquid ex ea commodi consequatur? Quis autem vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil molestiae consequatur, vel illum qui dolorem eum fugiat quo voluptas nulla pariatur?
</div>

<div id="block3" class="block">
  But I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system, and expound the actual teachings of the great explorer of the truth, the master-builder of human happiness. No one rejects, dislikes, or avoids pleasure itself, because it is pleasure, but because those who do not know how to pursue pleasure rationally encounter consequences that are extremely painful. Nor again is there anyone who loves or pursues or desires to obtain pain of itself, because it is pain, but because occasionally circumstances occur in which toil and pain can procure him some great pleasure. To take a trivial example, which of us ever undertakes laborious physical exercise, except to obtain some advantage from it? But who has any right to find fault with a man who chooses to enjoy a pleasure that has no annoying consequences, or one who avoids a pain that produces no resultant pleasure?
</div>

<button id="scroll-top-btn">👆</button>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

在实际站点上，该问题只是偶尔发生。单击左侧导航中的 anchor 链接时，滚动到顶部按钮会随着页面滚动而短暂闪烁。这种情况很难复制，并且遵循相同的步骤并不总是会发生，但在首次登陆常见问题解答页面并单击“疑难解答”链接时通常会发生这种情况。

如果我不运行 anchor 点击滚动功能，按钮不会闪烁。

我不明白为什么按钮会闪烁或者它取决于什么，因为它只会在页面滚动超过导航的高度(60px)后淡出。

我还使用 smoothState.js，它要求我在 $(document).ready 及其自身的 onAfter 上运行函数> 回调function，但滚动按钮监听器function仅在$(window).scroll上运行。

什么可能导致按钮闪烁问题以及如何解决该问题？

Answer 1

发生的情况是，当您加载页面时，滚动位置将位于最顶部。然后，当您单击 anchor 并且平滑滚动代码开始缓慢滚动页面时，将调用滚动监听器，但滚动位置仍将低于 navHeight ，因此它将淡出(隐藏) #scoll-top-btn按钮。

不久之后，滚动监听器将再次被调用，但这次滚动位置将高于 navHeight ，因此它将淡入(显示) #scoll-top-btn按钮。

您可以通过检查滚动方向和滚动位置来解决此问题，以便#scoll-top-btn按钮仅在向下滚动时显示或仅在向上滚动时隐藏。

另外，它看起来像你的 #scoll-top-btn按钮最初是可见的，所以我会添加 style="display: none"以便在页面加载时它始终隐藏(但这本身并不能解决您的问题)。

在这里您可以看到应用了这两个更改后它是如何工作的:

const navHeight = 42;
const $scrollTopBtn = $('#scroll-top-btn');

let lastScrollTop = 0;

$(window).scroll(function() {
  const scrollTop = $(document).scrollTop();
  const scrollUp = scrollTop < lastScrollTop;

  lastScrollTop = scrollTop;

  if (scrollTop > navHeight && !scrollUp) {
    $scrollTopBtn.stop().fadeIn();
  } else if (scrollTop < navHeight && scrollUp) {
    $scrollTopBtn.stop().fadeOut();
  }
});

$(document).ready(() => {
  $('a[href*="#"]').on('click', function(event) {
    const hash = this.hash;
    
    if (this.hash) {
      event.preventDefault();

      $('html, body').animate({
        scrollTop: $(hash).offset().top - navHeight,
      }, 350);

      window.location.hash = this.hash;
    }
  });
});

body {
  margin: 0;
  font-family: monospace;
}

nav {
  position: sticky;
  top: 0;
  display: flex;
  background: white;
  border-bottom: 2px solid black;
}

a {
  height: 40px;
  display: flex; 
  align-items: center; 
  padding: 0 8px;
  border-right: 2px solid black;
}

.block {
  min-height: 100vh;
  border-bottom: 2px solid black;
  display: flex; 
  justify-content: center;
  padding: 32px 50vw 32px 32px;
  box-sizing: border-box;
}

#scroll-top-btn {
  position: fixed;
  right: 8px;
  bottom: 8px;
  width: 40px;
  height: 40px;
  border: 2px solid black;
  display: flex; 
  align-items: center;
  justify-content: center;
  padding: 0;
  background: white;
}

<nav>
  <a href="#block1">Block 1</a>
  <a href="#block2">Block 2</a>
  <a href="#block3">Block 3</a>
</nav>

<div id="block1" class="block">
  Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</div>

<div id="block2" class="block">
  Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem. Ut enim ad minima veniam, quis nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut aliquid ex ea commodi consequatur? Quis autem vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil molestiae consequatur, vel illum qui dolorem eum fugiat quo voluptas nulla pariatur?
</div>

<div id="block3" class="block">
  But I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system, and expound the actual teachings of the great explorer of the truth, the master-builder of human happiness. No one rejects, dislikes, or avoids pleasure itself, because it is pleasure, but because those who do not know how to pursue pleasure rationally encounter consequences that are extremely painful. Nor again is there anyone who loves or pursues or desires to obtain pain of itself, because it is pain, but because occasionally circumstances occur in which toil and pain can procure him some great pleasure. To take a trivial example, which of us ever undertakes laborious physical exercise, except to obtain some advantage from it? But who has any right to find fault with a man who chooses to enjoy a pleasure that has no annoying consequences, or one who avoids a pain that produces no resultant pleasure?
</div>

<button id="scroll-top-btn" style="display: none">👆</button>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>