延迟使用Intersection Observer API转换元素

Question

我正在使用Intersection Observer API在用户滚动到内容时显示元素。 它运作良好，但我想延迟显示div ，如果有4个div's ，我希望第一个显示，接下来0.5秒显示下一个...不是全部在同一时间。 在示例中，效果也仅适用于第一class ，如果有多于1个class ，则它不适用于下一个img classes ，只适用于第一个img classes 。 您可以在本页底部看到该示例。

HTML

<section id="staff" style="padding-top: 100px;">
  <div class="col-lg-12 mx-auto mb-5">
    <div class="container">
      <div class="row icons-info">
        <div class="col-xs-12 col-sm-6 col-md-6 col-lg-3">
          <img class="floating show-bottom" src="img/Muñeco 1-08.png">
          <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nibh justo, tincidunt sed felis vitae, egestas scelerisque eros. </p>
        </div>
        <div class="col-xs-12 col-sm-6 col-md-6 col-lg-3 ">
          <img class="floating" src="img/Muñeco 2-08.png">
          <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nibh justo, tincidunt sed felis vitae, egestas scelerisque eros.</p>
        </div>
        <div class="col-xs-12 col-sm-6 col-md-6 col-lg-3 ">
          <img class="floating" src="img/Muñeco 3-08.png">
          <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nibh justo, tincidunt sed felis vitae, egestas scelerisque eros.</p>
        </div>
        <div class="col-xs-12 col-sm-6 col-md-6 col-lg-3">
          <img class="floating" src="img/Muñeco 1-08.png">
          <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nibh justo, tincidunt sed felis vitae, egestas scelerisque eros. </p>
        </div>
      </div>
    </div>
  </div>     
</section>

JS

// Instantiate a new Intersection Observer
let observer7 = new IntersectionObserver(onEntry7);
let staff = document.querySelector('.floating');

let element7 = document.querySelector("#staff p");
observer7.observe(element7);

function onEntry7(entry7) {
  if (entry7[0].isIntersecting) {
    staff.classList.add("show-bottom");
  }
}

CSS

.floating {opacity: 0; transition: 1s opacity;}
.floating.show-bottom {opacity: 1;  
  animation: movefromtop 1s alternate infinite;
  animation-iteration-count: 1;
  animation-fill-mode:  forwards;}
@keyframes movefromtop {
  from {
    transform: translateY(-5em);
  }
  to {
    transform: translateY(0em);
  }
}

Answer 1

使用querySelectorAll（）获取所有内部div元素，然后使用forEach为所有元素调用observer.observe()方法。 然后在观察者中，使用target属性查询内部图像并向其添加show-bottom类。

要在每个动画之间添加延迟，您必须通过返回Promise并使用setTimeout()来创建动画链。 如果交叉点对同一元素触发多次，请确保不要在动画中多次链接同一元素。 为此，使用animatedElements数组来跟踪被动画化的元素。

如果您只想为元素设置动画一次，则在开始相交后，您可以在观察者上调用unobserve以从其他交叉事件中取消注册。

注意：我编辑了您的HTML / CSS，使网格在片段中工作，以演示多个元素在同一行上时的连续动画效果。 我还在内部div中添加了一个with-img类，因此我们可以查询它们并将它们传递给observe方法。

 const onEntry7 = animateSequence('.floating', 'show-bottom'); const observer7 = new IntersectionObserver(onEntry7); const allElements7 = document.querySelectorAll('#staff div.with-img'); allElements7.forEach(e => observer7.observe(e)); function animateSequence(targetSelector, classToAdd, delay = 500) { const animatedElements = []; let chain = Promise.resolve(); function show(e) { return new Promise((res, rej) => { setTimeout(() => { e.classList.add(classToAdd); res(); }, delay); }); } return function(entries) { entries.forEach(entry => { if (entry.intersectionRatio > 0) { const elem = entry.target.querySelector(targetSelector); if (!animatedElements.includes(elem)) { animatedElements.push(elem); console.clear(); console.log('chaining', ...animatedElements.map(e => e.getAttribute('data--name'))); chain = chain.then(() => show(elem)); observer7.unobserve(entry.target); } } }) } } 

 .floating { opacity: 0; transition: 1s opacity; width: 157px; height: 220px; } .floating.show-bottom { opacity: 1; animation: movefromtop 1s alternate infinite; animation-iteration-count: 1; animation-fill-mode: forwards; } @keyframes movefromtop { from { transform: translateY(-5em); } to { transform: translateY(0em); } } section#staff { margin-top: 200px; margin-bottom: 200px; } 

 <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.0/css/bootstrap.min.css"> Scroll Down <section id="staff" style="padding-top: 100px;"> <div class="col-lg-12 mx-auto mb-5"> <div class="container"> <div class="row icons-info"> <div class="with-img col-xs-12 col-xs-6 col-sm-6 col-md-6 col-lg-3"> <img class="floating" src="https://lagaleramagazine.es/rucab/img/Muñeco 1-08.png" data--name="1"> <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nibh justo, tincidunt sed felis vitae, egestas scelerisque eros. </p> </div> <div class="with-img col-xs-12 col-xs-6 col-sm-6 col-md-6 col-lg-3 "> <img class="floating" src="https://lagaleramagazine.es/rucab/img/Muñeco 2-08.png" data--name="2"> <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nibh justo, tincidunt sed felis vitae, egestas scelerisque eros.</p> </div> <div class="with-img col-xs-12 col-xs-6 col-sm-6 col-md-6 col-lg-3 "> <img class="floating" src="https://lagaleramagazine.es/rucab/img/Muñeco 3-08.png" data--name="3"> <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nibh justo, tincidunt sed felis vitae, egestas scelerisque eros.</p> </div> <div class="with-img col-xs-12 col-xs-6 col-sm-6 col-md-6 col-lg-3"> <img class="floating" src="https://lagaleramagazine.es/rucab/img/Muñeco 1-08.png" data--name="4"> <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nibh justo, tincidunt sed felis vitae, egestas scelerisque eros. </p> </div> </div> </div> </div> </section>