# CheckBoxes RadioButton Behavior

You may want the checkbox to exhibit a non-standard, **RadioButton** behavior, where only one checkbox may be selected at a time and all previous checkbox selections are cleared. The example below defines the [OnClientNodeChecked](https://www.telerik.com/products/aspnet-ajax/documentation/controls/treeview/checkboxes/client-side) event. The **clientNodeChecked()** function that handles this event first retrieves the currently checked Node. Then checks if there is a previously checked Node in the "oldNode" global variable and unchecks it if so. The newly clicked Node is checked, and a reference to it is saved off in "oldNode" for later use the next time the [OnClientNodeChecked](https://www.telerik.com/products/aspnet-ajax/documentation/controls/treeview/checkboxes/client-side) event fires.

```JavaScript
<script type="text/javascript" language="javascript">

    var oldNode;
    function clientNodeChecked(sender, eventArgs) {
        var node = eventArgs.get_node();

        if (oldNode != null) {
            oldNode.set_checked(false);
        }

        node.set_checked(true);
        oldNode = node;
    }

    function pageLoad() {
        var tree = $find("<%= RadTreeView1.ClientID  %>");
        var checkedNodes = tree.get_checkedNodes();
        if (checkedNodes) {
            //this will ensure the correct behavior even if a node is checked server-side
            oldNode = checkedNodes[0];
        }
    }
</script>	    
```

```ASPNET
<telerik:RadTreeView RenderMode="Lightweight" ID="RadTreeView1" runat="server" CheckBoxes="True" OnClientNodeChecked="clientNodeChecked">
</telerik:RadTreeView>
```