Range: commonAncestorContainer property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨July 2015⁩.

The Range.commonAncestorContainer read-only property returns the deepest — or furthest down the document tree — Node that contains both boundary points of the Range. This means that if Range.startContainer and Range.endContainer both refer to the same node, this node is the common ancestor container.

Since a Range need not be continuous, and may also partially select nodes, this is a convenient way to find a Node which encloses a Range.

This property is read-only. To change the ancestor container of a Node, consider using the various methods available to set the start and end positions of the Range, such as Range.setStart() and Range.setEnd().

<ul>
  <li>
    Strings
    <ul>
      <li>Cello</li>
      <li>
        Violin
        <ul>
          <li>First Chair</li>
          <li>Second Chair</li>
        </ul>
      </li>
    </ul>
  </li>
  <li>
    Woodwinds
    <ul>
      <li>Clarinet</li>
      <li>Oboe</li>
    </ul>
  </li>
</ul>

CSS

The .highlight class created below uses a set of CSS @keyframes to animate a fading outline.

css

.highlight {
  animation: highlight linear 1s;
}

@keyframes highlight {
  from {
    outline: 1px solid red;
  }
  to {
    outline: 1px solid transparent;
  }
}

body {
  padding: 1px;
}

JavaScript

document.addEventListener("pointerup", (e) => {
  const selection = window.getSelection();

  if (selection.type === "Range") {
    for (let i = 0; i < selection.rangeCount; i++) {
      const range = selection.getRangeAt(i);
      playAnimation(range.commonAncestorContainer);
    }
  }
});

function playAnimation(el) {
  if (el.nodeType === Node.TEXT_NODE) {
    el = el.parentNode;
  }

  el.classList.remove("highlight");
  setTimeout(() => {
    el.classList.add("highlight");
  }, 0);
}