Go-generated alert (the server side)

func controller(rw http.ResponseWriter, r *http.Request) {
    var err error
//  err := errors.New("This is an error")
    str := "This is a test"
    t, _ := template.ParseFiles("index.html")
    t.Execute(rw, struct{
            Str string
            Err error
            }{str, err})
}