javascript - 滚动时尝试使用 jquery 使内容淡入

Question

我希望页面内容在向下滚动时淡入和在向上滚动时淡出，我使用了网站说明 ( https://www.superhi.com/blog/how-to-add-web-design-elements-that-fade-in-and-out-on-scroll ) 并尝试对其进行一些更改以适合我的元素，但它不起作用。我正在使用 Dreamweaver。

<script src="jquery-3.4.1.min.js"></script> 
<script src="fadein.js"></script>   
<script>

$(document).on("scroll", function () {
  var pageTop = $(document).scrollTop()
  var pageBottom = pageTop + $(window).height()
  var tags = $(".fade")

  for (var i = 0; i < tags.length; i++) {
    var tag = tags[i]

    if ($(tag).position().top < pageBottom) {
      $(tag).addClass("visible")
    } else {
      $(tag).removeClass("visible")
    }
  }
})

</script>   

<div id="content" style="margin:-8px;">
    <img src="images/n intro.jpg" style="width: 100%; margin-top:110px;" alt="intro image">
    <img class="fade" src="images/border.png" style="width:490px;  margin:40px; margin-left: 35%" alt="border line">

    <div id="mid">
    <h1  class="fade">Whether youre in it for...</h1>
    <img class="fade" src="images/photos/food&drink2.jpg" alt="picture of artistic coffee being made">  
    <p class="fade">The food and drink,</p>
    <img class="fade" src="images/photos/work2.jpg" alt="picture of laptop at a coffee table">
    <p class="fade">Getting some work done,</p>
    <img class="fade" src="images/photos/people2.jpg" alt="picture of a couples hands holding coffee">
    <p class="fade">The people,</p>
    <img class="fade" src="images/photos/book2.jpg" alt="picture of a book and coffee">
    <p class="fade">Or a good book,</p>
    <h2 class="fade">We got you covered!</h2>
    </div>

    <img class="fade" src="images/awards.png" style="display: block; margin-left:auto; margin-right: auto; width: 460px;" alt="three award icons">
    <ul>
        <li class="fade">Sustainable high quality coffee</li>
        <li class="fade">Comfortable seating</li>
        <li class="fade">A variety of table layouts to suit your needs</li>
        <li class="fade">High speed internet </li>
        <li class="fade">Charging ports provided</li>
    </ul>

</div>

.fade {
  opacity: 0;
}

.fade.visible {
  opacity: 1;
}

当我使用它时，页面只是正常显示所有内容，没有任何内容消失或不可见。

Answer 1

代码有几个问题:

1. 您指向 jQuery 的链接并未指向实际的 jQuery。我看了教程，是的，他们就是这么用的，但是你需要使用 CDN 链接: <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
2. fade.js只是他们用来放置 script 的名称你包括在内。你不一定需要那个。
3. 您需要添加 transition属性(property)给.fade类，否则，您不会看到它淡入或淡出，它只会从 0 opacity 切换。到 1(或全部)。

$(document).on("scroll", function () {
  var pageTop = $(document).scrollTop()
  var pageBottom = pageTop + $(window).height() - 20
  var tags = $(".fade")

  for (var i = 0; i < tags.length; i++) {
    var tag = tags[i]

    if ($(tag).position().top < pageBottom) {
      $(tag).addClass("visible")
    } else {
      $(tag).removeClass("visible")
    }
  }
});

.fade {
  opacity: 0;
  transition: all .3s ease;
}

.fade.visible {
  opacity: 1;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="content" style="margin:-8px;">
    <img src="images/n intro.jpg" style="width: 100%; margin-top:110px;" alt="intro image">
    <img class="fade" src="images/border.png" style="width:490px;  margin:40px; margin-left: 35%" alt="border line">

    <div id="mid">
    <h1  class="fade">Whether youre in it for...</h1>
    <img class="fade" src="images/photos/food&drink2.jpg" alt="picture of artistic coffee being made">  
    <p class="fade">The food and drink,</p>
    <img class="fade" src="images/photos/work2.jpg" alt="picture of laptop at a coffee table">
    <p class="fade">Getting some work done,</p>
    <img class="fade" src="images/photos/people2.jpg" alt="picture of a couples hands holding coffee">
    <p class="fade">The people,</p>
    <img class="fade" src="images/photos/book2.jpg" alt="picture of a book and coffee">
    <p class="fade">Or a good book,</p>
    <h2 class="fade">We got you covered!</h2>
    </div>

    <img class="fade" src="images/awards.png" style="display: block; margin-left:auto; margin-right: auto; width: 460px;" alt="three award icons">
    <ul>
        <li class="fade">Sustainable high quality coffee</li>
        <li class="fade">Comfortable seating</li>
        <li class="fade">A variety of table layouts to suit your needs</li>
        <li class="fade">High speed internet </li>
        <li class="fade">Charging ports provided</li>
    </ul>

</div>

这是一个可以玩的 fiddle : https://jsfiddle.net/t4Ljnk7v/1/

我更新了 pageBottom变量，这样您就可以在到达底部时看到底部元素淡入。