Apart script that require input embedded in the Django templates, Javascript code should be handled by webpack.

Thus this implementation should be moved in the file assets/src/bundles/webapp/webapp-utils.js at the end of the $(document).ready() callback starting at line 58.

All JS code handled by webpack can use jQuery and ES6 syntax so I would rather use the following implementation here:

let scrollThreshold = 0;
scrollThreshold += $('.swh-top-bar').height() || 0;
scrollThreshold += $('.navbar').height() || 0;
$(window).scroll(() => {
  if ($(window).scrollTop() > scrollThreshold) {
    $('#back-to-top').css('display', 'block');
  } else {
    $('#back-to-top').css('display', 'none');
  }
});