Show only children relative to current page

Question

I have this structure section:

1.0 Nav point level 1
  1.1 Nav point level 2
  1.2 Nav point level 2
  1.3 Nav point level 2
2.0 Nav Point level 1
3.0 Nav Point level 1

I want to show only top level points as long as there is no children ont the current page.

Example:

When im on page 1.0 Nav point level 1 the navi shoud look like above (Because the current page has descendants).

But when im on 2.0 Nav Point level 1 the navi should look like this: (Everything below level 1 not visible because the current page has no children.)

1.0 Nav point level 1
2.0 Nav Point level 1
3.0 Nav Point level 1

I tried to wrap the children tag into a conditional. But that's not allowed:

{% set topLevel = (entry.level == 1) ? entry : entry.getAncestors().level(1).first()  %}


{% if topLevel.hasDescendants %}

  <nav class="subNav">

    <ul>

      {% set subnav =  topLevel.getDescendants()  %}

      {% nav page in subnav  %}
        <li>
            <a href="{{ page.url }}">{{ page.title }}</a>
            {% if entry.hasDescendantes %} // this does not work at all.
              {% ifchildren %}
                <ul>{% children %}</ul>
              {% endifchildren %}
            {% endif %}
        </li>
      {% endnav %}

    </ul>

  </nav>
{% endif %}

I can't wrap my head around it.

Answer 1

Don't use the nav tag. Assuming a structure called pages, try something like this:

{% set pages = craft.entries.section('pages').level(1).all() %}
<ul>
{% for page in pages %}
    <li>
        {{ page.title }}
        {% if entry is defined and entry.hasDescendants %}
            {% set children = page.getChildren() %}
            <ul>
            {% for child in children %}
                <li>{{ child.title }}</li>
            {% endfor %}
            </ul>
        {% endif %}
    </li>
{% endfor %}
</ul>