code: func (r JsonpJSON) Render(w http.ResponseWriter) (err error) {
  	r.WriteContentType(w)
  	ret, err := json.Marshal(r.Data)
  	if err != nil {
  		return err
  	}
  
  	if r.Callback == "" {
  		_, err = w.Write(ret)
  		return err
  	}
  
  	callback := template.JSEscapeString(r.Callback)
  	_, err = w.Write([]byte(callback))
  	if err != nil {
  		return err
  	}
  	_, err = w.Write([]byte("("))
  	if err != nil {
  		return err
  	}
  	_, err = w.Write(ret)
  	if err != nil {
  		return err
  	}
  	_, err = w.Write([]byte(")"))
  	if err != nil {
  		return err
  	}
  
  	return nil
  }
docs: // Render (JsonpJSON) marshals the given interface object and writes it and its callback with custom ContentType.