Auto expand child when parent checked on treelist using javascript -

can teach me how expand child item on tree list when parent item checked in javascript?

current,i had function on javascript check/unchecked parent item , child item. function fail auto expand child item when parent item checked. can lead me hand please?

here javascript.

  var parenitemselected = false;          function onclientnodeclicked(sender, args) {              var currnode = args.get_item();              var childnodes = currnode.get_childitems();              var nodecount = currnode.get_childitems().length;              var parentitem = currnode.get_parentitem();                if (parentitem) {                    parenitemselected = true;                  parentitem.set_selected(true);              }                if (currnode.get_selected()) {                  checkallchildren(childnodes, nodecount);              }              else {                  uncheckallchildren(currnode, childnodes, nodecount);              }              parenitemselected = false;          }            function uncheckallchildren(currnode, nodes, nodecount) {              var i;              (i = 0; < nodecount; i++) {                  nodes[i].set_selected(false);              }              currnode.set_selected(false);          }            function checkallchildren(nodes, nodecount) {              var i;                if (!parenitemselected) {                  (i = 0; < nodecount; i++) {                      nodes[i].set_selected(true);                  }              }          }

code c# or vb.net welcome.

thanks.