# OnClientNodeExpanding

The **OnClientNodeExpanding** client-side event occurs when the user clicks the expand (plus) button. The event is called just prior to postback or URL redirection and can be canceled.

> caution Calling the client-side **expand()** or **set_expanded(true)** method does not fire **OnClientNodeExpanding** and **OnClientNodeExpanded** client-side events. More information is available [here](https://www.telerik.com/products/aspnet-ajax/documentation/controls/treeview/troubleshooting/expanding-nodes).

The event handler receives parameters:

1. The **TreeView** instance that fired the event.

2. Event arguments with functions:

* **get_node()** retrieves a reference to the clicked on node.

* **set_cancel()** - call this function to specify whether the event should be canceled (true) or not (false).

* **get_domEvent()** retrieves a DOM event object of the node expand.

The example below shows how to prevent expanding a "Recent Searches" node. Note that the **OnClientNodeExpanded** event does not fire when the expand (plus) button is clicked.

```ASPNET
<telerik:RadTreeView RenderMode="Lightweight" ID="RadTreeView1" runat="server" AllowNodeEditing="True" 
                     OnClientNodeExpanded="ClientNodeExpanded"
                     OnClientNodeExpanding="ClientNodeExpanding">
</telerik:RadTreeView>
```

```JavaScript
function ClientNodeExpanded(sender, eventArgs)
{
	alert("OnClientNodeExpanded");
}
function ClientNodeExpanding(sender, eventArgs)
{

	var node = eventArgs.get_node();    
	if(node.get_text() == "Recent Searches")
	{
		eventArgs.set_cancel(true);
	}
}  
```

## See Also

* [OnClientNodeExpanded](https://www.telerik.com/products/aspnet-ajax/documentation/controls/treeview/client-side-programming/events/onclientnodeexpanded)

* [RadTreeNode](https://www.telerik.com/products/aspnet-ajax/documentation/controls/treeview/client-side-programming/objects/radtreenode)

* [Expanding Nodes](https://www.telerik.com/products/aspnet-ajax/documentation/controls/treeview/troubleshooting/expanding-nodes)