using 'this' key word with drop down list in ASPX page

I have an aspx page. On this page datagrid, the last column of the grid has a drop down list.
When the user changes the value of the drop down list I want an event to fire in javascript.

my code behind file has the following code in the itemdatabound event:
Cbo.Attributes.Add("onchange", "SelectedPremium( this );")
When the event fires I get the following error message:Microsoft JScript runtime error: Object expected

The 'This' key word does not want to work. How can I dynamcially reference the control since I won't know the name until the form is rendered on the users screen?

Thank you for your assistance.

I found the error. The header did not contain the link to the js file. No javascript was working on the form!