How I made toggle transition to element

The HTML <details> element provides a simple way to create expandable and collapsible content sections. Let's explore how to enhance this functionality with smooth CSS transitions, and address the limitations of using CSS alone.

A basic <details> implementation looks like this:

<details>
  <summary>Click to expand</summary>
  <p>This is the content.</p>
</details>

While this works, adding a smooth transition using only CSS proves challenging. The following CSS, for instance, doesn't produce the desired effect:

details#my-details {
  transition-duration: 300ms;
}

To achieve a smooth toggle transition, JavaScript is necessary.

Solution

The key is to wrap the content within the <details> element with another element (here, a <div>). This allows us to target and animate the content separately:

<details id="my-details">
  <summary>Click to expand</summary>
  <div>
    <p>This is the content.</p>
  </div>
</details>

The following JavaScript code then handles the animation:

const details = document.getElementById("my-details");
const summary = details.firstElementChild;
const content = summary.nextElementSibling;
let isAnimating = false;

summary.onclick = (ev) => {
  ev.preventDefault();
  if (isAnimating) return;

  const contentHeight = content.getBoundingClientRect().height;
  isAnimating = true;

  // Closing <details>
  if (details.open) {
    return content
      .animate(
        { height: [contentHeight + 'px', '0px'] },
        { duration: 300 }
      )
      .finished
      .then(() => details.open = isAnimating = false);
  }

  // Opening <details>
  details.open = true;
  content.animate(
    { height: ['0px', contentHeight + 'px'] },
    { duration: 300 }
  ).finished.then(() => isAnimating = false);
};

This JavaScript code uses the animate() method to control the height transition of the content wrapper. Note that in some cases, adding overflow: hidden; to the content wrapper's CSS may be needed for optimal results.

Explanation

The JavaScript code prevents the default <summary> behavior, gets the content height, and then uses the animate() method to smoothly adjust the height based on whether the <details> is opening or closing. The isAnimating variable prevents multiple animations from running concurrently.

The `isAnimating` Variable

The isAnimating flag ensures that only one animation runs at a time, preventing conflicts and unexpected behavior if the user clicks repeatedly while an animation is in progress.

Conclusion

This technique provides a smooth, controlled transition for the <details> element. While this example uses height animation, the animate() method can be adapted to animate other CSS properties, offering a versatile approach to creating engaging user interactions. Remember that a deeper dive into the animate() method and its capabilities is recommended for more advanced animations.

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