grafana/k6 · error

unsupported responseCallback

Error message

unsupported responseCallback

What it means

parseRequest saw a non-null 'responseCallback' entry in the per-request params object whose value is not an object produced by http.expectedStatuses. Only null (disable) or an expectedStatuses result are accepted; anything else — a plain function, string, or arbitrary object — hits this guard.

Source

Thrown at js/modules/k6/http/request.go:420

					return nil, fmt.Errorf("invalid timeout value: %w", err)
				}
				result.Timeout = t
			case "throw":
				result.Throw = params.Get(k).ToBoolean()
			case "responseType":
				responseType, err := httpext.ResponseTypeString(params.Get(k).String())
				if err != nil {
					return nil, err
				}
				result.ResponseType = responseType
			case "responseCallback":
				v := params.Get(k).Export()
				if v == nil {
					result.ResponseCallback = nil
				} else if c, ok := v.(*expectedStatuses); ok {
					result.ResponseCallback = c.match
				} else {
					return nil, fmt.Errorf("unsupported responseCallback")
				}
			}
		}
	}

	if result.ActiveJar != nil {
		httpext.SetRequestCookies(result.Req, result.ActiveJar, result.Cookies)
	}

	return result, nil
}

func (c *Client) prepareBatchArray(requests []any) (
	[]httpext.BatchParsedHTTPRequest, []*Response, error,
) {
	reqCount := len(requests)
	batchReqs := make([]httpext.BatchParsedHTTPRequest, reqCount)
	results := make([]*Response, reqCount)

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Pass the result of http.expectedStatuses(...), e.g. { responseCallback: http.expectedStatuses(200, 300-399) }
2. Set responseCallback: null to disable the callback instead of using a function or other value

When it happens

Trigger: Thrown at js/modules/k6/http/request.go:420 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/f7ef253ea767914d. Report an issue: GitHub.