title: jstree - stop single expanded node from collapsing
body: <p>Using <a href="https://www.jstree.com" rel="nofollow noreferrer">jstree</a> is it possible to block the collapse of a single specific node?</p>
  
  <p>I have a tree structure which can be expanded/collapsed at will... but I have certain nodes that should always be open and not allow the user to collapse them.</p>
  
  <p>Is there a way to block the collapse (maybe through the <code>data-jstree</code> attribute on the <code>&lt;li&gt;</code>)... and if possible, a way to also remove the triangle against the item?</p>
  
  <p>I've tried hooking into the <code>close_node.jstree</code> event but neither using a <code>return false</code> or <code>e.preventDefault()</code> is stopping it happening.</p>
  
  <p>In the following example, I want the "Item 2 - Must Keep Open" to ALWAYS be open, and not allow the user to hide the "Always Visible" item...</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>$(function() {
    $("#treeRoot").jstree({
      core: {
        themes: {
          variant: "small"
        }
      }
    });
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;link href="https://cdnjs.cloudflare.com/ajax/libs/jstree/3.2.1/themes/default/style.min.css" rel="stylesheet"/&gt;
  &lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"&gt;&lt;/script&gt;
  &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/jstree/3.2.1/jstree.min.js"&gt;&lt;/script&gt;
  &lt;div id="treeRoot"&gt;
    &lt;ul&gt;
      &lt;li data-jstree='{"opened":true}'&gt;Root
        &lt;ul&gt;
          &lt;li&gt;Item 1&lt;/li&gt;
          &lt;li data-jstree='{"opened":true}'&gt;Item 2 - Must keep open
            &lt;ul&gt;
              &lt;li&gt;Always Visible&lt;/li&gt;
            &lt;/ul&gt;
          &lt;/li&gt;
          &lt;li&gt;Item 3&lt;/li&gt;
        &lt;/ul&gt;
      &lt;/li&gt;
    &lt;/ul&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>