How to call Javascript functions from Silverlight code ?

<script language="javascript"≫
function SayHello() 
{
       alert("Hello from JavaScript, invoked by Silverlight");
} 
</script>

<Grid x:Name="LayoutRoot" Background="White">
<Button x:Name="btnSayHello" Content="Say Hello" 
     Click="btnSayHello_Click"></Button>
</Grid>

private void btnSayHello_Click(object sender, RoutedEventArgs e)
{
    HtmlPage.Window.Invoke("SayHello");
}

using System.Windows.Browser;