multiple javascript observers for adding classes to multiple elements

user_4881971 0
Viewed 61

I have a short javascript function which applies an animation class to a div when it is "scrolled" into view. This works great for one div with these classes. But how do I apply this to multiple elements with these classes? I have multiple elements of .square and .square-wrapper down the page, and I want each one to animate in when the user scrolls near it. Here is the function which only applies .square-animate to the first element :

<script>
const observer = new IntersectionObserver(entries => {
  entries.forEach(entry => {
    const square = entry.target.querySelector('.square');

    if (entry.isIntersecting) {
      square.classList.add('square-animation');
      return; // if we added the class, exit the function
    }

    // We're not intersecting, so remove the class!
    square.classList.remove('square-animation');
   });
 });

 observer.observe(document.querySelector('.square-wrapper'));

 </script>

The HTML part looks something like this:

<div class="container row square-wrapper">
    <div class="col s12 m4 square">
    // some content here 
    </div>
</div>

<div class="container row square-wrapper">
    <div class="col s12 m4 square">
    // some content here 
    </div>
</div>

<div class="container row square-wrapper">
    <div class="col s12 m4 square">
    // some content here 
    </div>
</div>
html javascript
1 Answers

I don't know if there is a smartest solution. In this mine, I call observe on each target element that you want observe. The various calls don't override the previous one, but listen to all.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .square-animation {
        animation: coloraGraduale 2s forwards;
      }

      @keyframes coloraGraduale {
        from {
          background-color: white;
        }
        to {
          background-color: red;
        }
      }
    </style>
  </head>
  <body>
    <div style="height: 1000px"></div>
    <div class="container row square-wrapper">
      <div class="col s12 m4 square">
        <p>
          Lorem ipsum dolor sit amet consectetur adipisicing elit. Perspiciatis
          fuga dolore impedit architecto cupiditate dignissimos rerum ut
          deleniti. Laudantium harum expedita a. Eius velit dolorum laborum modi
          quidem voluptate ullam!
        </p>
      </div>
    </div>

    <div class="container row square-wrapper">
      <div class="col s12 m4 square">
        <p>
          Lorem ipsum dolor sit amet consectetur adipisicing elit. Perspiciatis
          fuga dolore impedit architecto cupiditate dignissimos rerum ut
          deleniti. Laudantium harum expedita a. Eius velit dolorum laborum modi
          quidem voluptate ullam!
        </p>
      </div>
    </div>

    <div class="container row square-wrapper">
      <div class="col s12 m4 square">
        <p>
          Lorem ipsum dolor sit amet consectetur adipisicing elit. Perspiciatis
          fuga dolore impedit architecto cupiditate dignissimos rerum ut
          deleniti. Laudantium harum expedita a. Eius velit dolorum laborum modi
          quidem voluptate ullam!
        </p>
      </div>
    </div>

    <script>
      const observer = new IntersectionObserver((entries) => {
        entries.forEach((entry) => {
          const square = entry.target.querySelector(".square");

          if (entry.isIntersecting) {
            square.classList.add("square-animation");
            return; // if we added the class, exit the function
          }

          // We're not intersecting, so remove the class!
          square.classList.remove("square-animation");
        });
      });

      let elements = document.querySelectorAll(".square-wrapper");
      for (let element of elements) {
        observer.observe(element);
      }
    </script>
  </body>
</html>

user_41108260
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