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                <ul id="treelist">
  <li>Layer 1 Element
      <li>Layer 2 Element
          <li>Layer 3 Element</li>


                .section {
  margin: 50px 0;

.list-heading {
  font-weight: bold;
  cursor: pointer;

ul > li {
  font-weight: normal;
  cursor: auto;



                // umschließt den Text aus dem li Element in einen span Tag, damit der span Tag nicht per Hand eingegeben werden muss
for (let item of treelist.querySelectorAll("li")) {
  if (!item.querySelector("ul")) continue;

  const itemSpan = document.createElement("span");


treelist.onclick = (event) => {
  // Wenn nicht auf einen span Tag geklickt wurde wird die
  // Function verlassen
  if ( != "SPAN") return;

  // selektiert alle Unterlisten des angelickten Elements
  const childlists ="ul");

  // verlässt die Funktion wenn es keine Unterlisten gibt
  if (!childlists) return;

  // macht alle Unterlisten unsichtbar
  childlists.hidden = !childlists.hidden;