js

addEventListener("close", (event) => {});

onclose = (event) => {};

html

<dialog class="example-dialog">
  <form method="dialog">
    <button>Close via method="dialog"</button>
  </form>
  <button class="close">Close via .close() method</button>
  <p>Or hit the <kbd>Esc</kbd> key</p>
</dialog>

<button class="open-dialog">Open dialog</button>

<div class="result"></div>

js

const result = document.querySelector(".result");

const dialog = document.querySelector(".example-dialog");
dialog.addEventListener("close", (event) => {
  result.textContent = "dialog was closed";
});

const openDialog = document.querySelector(".open-dialog");
openDialog.addEventListener("click", () => {
  dialog.showModal();
  result.textContent = "";
});

const closeButton = document.querySelector(".close");
closeButton.addEventListener("click", () => {
  dialog.close();
});