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HTML

CSS

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HTML

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

CSS

              
                .section {
  margin: 50px 0;
}

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

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

              
            
!

JS

              
                // 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");
  item.prepend(itemSpan);
  itemSpan.append(itemSpan.nextSibling);

  itemSpan.classList.add("list-heading");
}

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

  // selektiert alle Unterlisten des angelickten Elements
  const childlists = event.target.parentNode.querySelector("ul");

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

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

              
            
!
999px

Console