Add or remove a class depending on an element's display [closed]

i want to add a class to body if #myModal's display is block and remove the class when #myModal's display changes to none. I applied the following code but it isn't working.

<script>
  var body = document.body
  var modal = document.getElementById('myModal')
  if (modal.style.display = 'block') {
    body.classList.add('hide');
  }
  if (modal.style.display == 'none') {
    body.classList.remove('hide');
  }
</script>