javascript - 如何在窗口滚动时向事件 div 添加动画？

Question

我的页面中有多个 div。该 div 包含大小和颜色。向下滚动时，屏幕可见的 div 应向上移动，向上滚动时，应返回到其原始位置。

这是迄今为止我尝试过的代码。使用此代码，当我向下滚动时，div 向上移动，但当我向上滚动时，div 不会向下移动。有人可以帮我吗？

function isElementInViewport(el) {
  if (typeof jQuery === "function" && el instanceof jQuery) {
    el = el[0];
  }
  var rect = el.getBoundingClientRect();
  return (
    (rect.top <= 0 &&
      rect.bottom >= 0) ||
    (rect.bottom >= (window.innerHeight || document.documentElement.clientHeight) &&
      rect.top <= (window.innerHeight || document.documentElement.clientHeight)) ||
    (rect.top >= 0 &&
      rect.bottom <= (window.innerHeight || document.documentElement.clientHeight))
  );
}

window.addEventListener('scroll', function(e) {

  winScrollTop = $(this).scrollTop();

  var elementsToShow = document.querySelectorAll('.rectangle');
  Array.prototype.forEach.call(elementsToShow, function(element) {
    if (isElementInViewport(element)) {
      element.classList.add('is-visible');
    } else {
      element.classList.remove('is-visible');
    }
  });
});

.rectangle {
  background-color: red;
  height: 444px;
  width: 100px;
  /* margin-top: -98px; */
  z-index: -30;
  transition: 0.5s;
  transform: translateY(-98px);
  margin-bottom: 25px;
}

.is-visible {
  transform: translateY(-250px);
}

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

Answer 1

所以我在这里所做的是，首先检查滚动事件，然后确定滚动实际上是向上还是向下。一旦我确定了我是向上还是向下滚动，我就分别添加了这些类。对于不可见的类，我设置样式转换:translateY(0px)，它只是将元素返回到其默认位置。

.not-visible{
  transform: translateY(0px);
}


var lastScrollTop= 0;
window.addEventListener('scroll', function(e) {
  winScrollTop = $(this).scrollTop();

  var st = window.pageYOffset || document.documentElement.scrollTop; // Credits:
  var elementsToShow = document.querySelectorAll('.rectangle');
     if (st > lastScrollTop){ // If st is greater than lastscrollTop then it is downward
      console.log("down");

       // then check if elemetnts are in view
       Array.prototype.forEach.call(elementsToShow, function(element) { 
            if (isElementInViewport(element)) {

              element.classList.remove('not-visible'); // remove class notvisible if any
              element.classList.add('is-visible'); // Add class isvisible 
            }
               lastScrollTop = st <= 0 ? 0 : st; // For Mobile or negative scrolling

       });
    } else {
      console.log("up");

       Array.prototype.forEach.call(elementsToShow, function(element) { 
           if (isElementInViewport(element)) {
              // Remove class isvisible and add class not visible to move the element to default place
              element.classList.remove('is-visible'); 
              element.classList.add('not-visible');
           }
              lastScrollTop = st <= 0 ? 0 : st; // For Mobile or negative scrolling

       });

    }


});