title: Why closing a page does not unmount the component
body: <p>I know there is normally <code>unmounting</code> the child in a parent and it's not okay to <code>unmount</code> a child itself. But I am just curious about it that why the <code>unloading</code> (closing the page) will not trigger the <code>unmount</code> event. Something interesting behind this design? I looked around but found nothing till now. </p>
  
  <p>Thank you for any idea provided here! </p>
  
  <p>Best wishes, Hearen.</p>