在进入视口时将事件添加到元素列表

Question

我在页面上有很多元素，我使用函数来检查是否是视口上的元素，如果有的话，添加一些带动画的类。但是如何将事件添加到certaine元素而不是所有元素。 codpen

＆＃13;

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function isElementInViewport(elem) {
      var $elem = $(elem);

      // Get the scroll position of the page.
      var scrollElem = ((navigator.userAgent.toLowerCase().indexOf('webkit') != -1) ? 'body' : 'html');
      var viewportTop = $(scrollElem).scrollTop();
      var viewportBottom = viewportTop + $(window).height();

      // Get the position of the element on the page.
      var elemTop = Math.round($elem.offset().top);
      var elemBottom = elemTop + $elem.height();

      return ((elemTop < viewportBottom) && (elemBottom > viewportTop));
  }

function checkAnimation() {
        var $newsArrowRight = $('.box .arrow');
//         for (var i = 0; i < $newsArrowRight.length; i++) {
//           // if ($newsArrowRight.hasClass('fade-in-right-js')) return;
//           if(isElementInViewport($newsArrowRight[i])){
//             console.log($newsArrowRight[i]);
//             $newsArrowRight[i].addClass('fade-in-right-js');
//           }

//         }
        // $.map( $newsArrowRight, function(e) {
        //   if (e.hasClass('fade-in-right-js')) return;
        //   if(isElementInViewport(e)){
        //     e.addClass('fade-in-right-js');
        //   }
        // });
        if ($newsArrowRight.hasClass('fade-in-right-js')) return;
        //
        if(isElementInViewport($newsArrowRight)){
          $newsArrowRight.addClass('fade-in-right-js');
        }
        
    }

    // Capture scroll events
    $(window).scroll(function() {
        checkAnimation();
    });

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.box {
  height: 40vh;
  width: 20vh;
  background: green;
  margin-bottom: 1rem;
  position: relative;
}
.box .arrow {
  position: absolute;
  bottom: 0;
  font-size: 20px;
  color: white;
  transform: translateX(-90px);
}
.box .arrow.fade-in-right-js {
  transform: translateX(0);
  opacity: 1;
  -webkit-animation: fade-in-right 1s ease-in-out;
  -moz-animation: fade-in-right 1s ease-in-out;
  -ms-animation: fade-in-right 1s ease-in-out;
  -o-animation: fade-in-right 1s ease-in-out;
  animation: fade-in-right 1s ease-in-out;
}
@-moz-keyframes fade-in-right {
  0% {
    transform: translateX(-90px);
    opacity: 0;
  }
  100% {
    transform: translateX(0);
    opacity: 1;
  }
}
@-webkit-keyframes fade-in-right {
  0% {
    transform: translateX(-90px);
    opacity: 0;
  }
  100% {
    transform: translateX(0);
    opacity: 1;
  }
}

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<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">Text</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">text</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">text</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">text</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">text</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">arrow</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">arrow</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">arrow</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">arrow</div>
</div>
<div class="box">
  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsa!
  <div class="arrow">arrow</div>
</div>

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Answer 1

解决方案是每个codpen

   function checkAnimation() {
    var $newsArrowRight = $.find('.box .arrow');
    $.each($newsArrowRight, function() {
      var element = $(this);
      if (element.hasClass('fade-in-right-js')) return;

      if(isElementInViewport(element)){
      element.addClass('fade-in-right-js');
    }
    });
}

// Capture scroll events
$(window).scroll(function() {
    checkAnimation();
});