Detect if the browser tab is being closed by the user

detectBrowserClosing.html

<script type="text/javascript">
window.addEventListener('beforeunload', function(e) {
  e.preventDefault();
  e.returnValue = '';
});
</script>

<b>Detect browser or tab closing</b>

    <p>
      The beforeunload function is triggered
      just before the browser or tab is to be
      closed or the page is to be reloaded.
      Modern browsers require some interaction
      with the page, otherwise the dialog box
      is not shown.
    </p>

    <form>
      <textarea placeholder="Trigger an interaction by writing something here"></textarea>
    </form>

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