code: func (c *Ctx) JSONP(code int, i interface{}, callback string) (err error) {
  
  	b, e := json.Marshal(i)
  	if e != nil {
  		err = e
  		return
  	}
  
  	c.response.Header().Set(ContentType, ApplicationJavaScriptCharsetUTF8)
  	c.response.WriteHeader(code)
  
  	if _, err = c.response.Write([]byte(callback + "(")); err == nil {
  
  		if _, err = c.response.Write(b); err == nil {
  			_, err = c.response.Write([]byte(");"))
  		}
  	}
  
  	return
  }
docs: // JSONP sends a JSONP response with status code and uses `callback` to construct
  // the JSONP payload.