AEM: Add JavaScript (including events) to AEM loaded on editor.html. Solution: Create clientlib with category "cq.authoring.dialog". Exemplary usage: Reload page if layer changes.

.content.xml

<?xml version="1.0" encoding="UTF-8"?>
<jcr:root xmlns:cq="http://www.day.com/jcr/cq/1.0" xmlns:jcr="http://www.jcp.org/jcr/1.0"
          jcr:primaryType="cq:ClientLibraryFolder"
          categories="[cq.authoring.dialog]"/>

AEM.on-layer-change.js

(function () {
  'use strict';

  function onModeChange() {
    location.reload();
  }

  function reloadOnModeChange() {
    document.querySelectorAll('.js-editor-LayerSwitcherTrigger').forEach(function (element) {
      element.addEventListener('click', onModeChange);
    });
  }

  reloadOnModeChange();
}());