Telerik RadComboBox selected value using jquery in external js file

Question

I have a Telerik RadComboBox and need to get the selected value (not text) from it.

My problem is I need to get it in an external javascript file so I cannot use the

var comboBox = $find("<%= RadComboBox1.ClientID %>"); 
var selectedValue = comboBox.get_value();

I can get the text from the external javascript file using jquery by doing

$('#RadComboBox1').val();

but I cannot get the value.