title: How to get all checked nodes in jstree?
body: <p>I need to export my nodes like this:</p>
  
  <pre><code>function recursive_simplify(node){ 
      if(node.children){
          for(var i =0;i&lt;node.children.length;i++){
              node.children[i] = recursive_simplify(node.children[i])
          }
      }
      delete node['metadata'];
      return node
  }
  
  $('body').on('click','.data-export', function () {
      var tree=$.jstree._reference('#reference-data-exchange');
      var checked = tree.get_checked(); 
      var result = [];
      for(var i=0, checkedLength = checked.length; i&lt;checkedLength;i++)
      {
        var checkedJson = tree.get_json(checked[i],['id','rel','data-bin','data-pos'])[0];
        checkedJson = recursive_simplify(checkedJson);
        result.push(checkedJson);
      }
      alert(JSON.stringify(result));
  });
  </code></pre>
  
  <p>it's works fine, BUT! I need all checked nodes(checked &amp; undetermined)
  My code returns only checked.
  Plz help.</p>