Gridview confirm checkbox javascript problem

I want to confirm with javascript checked true before triggering checkedChanged event on server side

this is filling checkbox in edit mode

private void potvrdaGreskaReprint(GridViewRowEventArgs e)
    {
        CheckBox ch = (CheckBox)e.Row.FindControl("cbGreska");
        ch.Attributes.Add("onclick", "confirmation(" + ch.UniqueID + ")");
    }

next is javascript function:



defining checkbox in gridview:


                   
                       
                   
                   
                       
                       
                   
                   
               

Finally checked changed event on server side

protected void cbGreska_OnCheckedChanged(object sender, EventArgs e)
    {
        CheckBox ch = (CheckBox)sender;


        if (ch.Checked)
        {......


So basicly I want to trigger checked Changed event with javascript

On debugging I get "Error: Object doesn't support property or method 'replace' "

at   __doPostBack(checkbox, ''); line in javascript function