HTMLDialogElement: returnValue property

<dialog id="dialog">
  <p>Do you agree to the Terms of Service (link)?</p>
  <button id="decline" value="declined">Decline</button>
  <button id="accept" value="accepted">Accept</button>
</dialog>
<button id="open">Open dialog</button>

<pre id="log"></pre>

#log {
  height: 170px;
  overflow: scroll;
  padding: 0.5rem;
  border: 1px solid black;
}

const logElement = document.getElementById("log");
function log(text) {
  logElement.innerText = `${logElement.innerText}${text}\n`;
  logElement.scrollTop = logElement.scrollHeight;
}

const dialog = document.getElementById("dialog");
const openButton = document.getElementById("open");
const declineButton = document.getElementById("decline");
const acceptButton = document.getElementById("accept");

openButton.addEventListener("click", () => {
  // Reset the return value on each open
  dialog.returnValue = "";
  updateReturnValue();
  // Show the dialog
  dialog.showModal();
});

function closeDialog(event) {
  const button = event.target;
  dialog.close(button.value);
}

function updateReturnValue() {
  log(`Return value: "${dialog.returnValue}"`);
}

declineButton.addEventListener("click", closeDialog);
acceptButton.addEventListener("click", closeDialog);

dialog.addEventListener("close", updateReturnValue);