How to writ Java Script function to fire server side button click evet without manually click that buttong

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ASP.NET

Javascript

I want to pop up the ajax modat popup extender when the user click one of the radio button list's item. That radio list buttons are located inside the gridview as Item template. From the pop up , let the user choose some options and enter some data. When user click ok button from the pop up box, the values that user key in are taken back to server side datagrid.