Selection: containsNode() method

containsNode(node)
containsNode(node)
containsNode(node, partialContainment)

console.log(window.getSelection().containsNode(document.body, true));

<p>Can you find the secret word?</p>
<p>Hmm, where <span id="secret">SECRET</span> could it be?</p>
<p id="win" hidden>You found it!</p>

#secret {
  color: transparent;
}

const secret = document.getElementById("secret");
const win = document.getElementById("win");

// Listen for selection changes
document.addEventListener("selectionchange", () => {
  const selection = window.getSelection();
  const found = selection.containsNode(secret);

  win.toggleAttribute("hidden", !found);
});