grafana/k6 · error

unsupported argument, expected http.expectedStatuses

Error message

unsupported argument, expected http.expectedStatuses

What it means

SetResponseCallback received a non-null value that is not an expectedStatuses object. The value exported from the Sobek VM did not type-assert to *expectedStatuses — e.g. a user-supplied function or plain object was assigned to http.setResponseCallback instead of the documented expectedStatuses result or null.

Source

Thrown at js/modules/k6/http/response_callback.go:91

			result.minmax = append(result.minmax, [2]int{int(minValue.ToInteger()), int(maxValue.ToInteger())})
		}
	}
	return &result
}

// SetResponseCallback sets the responseCallback to the value provided. Supported values are
// expectedStatuses object or a `null` which means that metrics shouldn't be tagged as failed and
// `http_req_failed` should not be emitted - the behaviour previous to this
func (c *Client) SetResponseCallback(val sobek.Value) {
	if val != nil && !sobek.IsNull(val) {
		// This is done this way as ExportTo exports functions to empty structs without an error
		if es, ok := val.Export().(*expectedStatuses); ok {
			c.responseCallback = es.match
		} else {
			common.Throw(
				c.moduleInstance.vu.Runtime(),
				fmt.Errorf("unsupported argument, expected http.expectedStatuses"),
			)
		}
	} else {
		c.responseCallback = nil
	}
}

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Pass the value returned by http.expectedStatuses(...), e.g. http.setResponseCallback(http.expectedStatuses(200-299))
2. Pass null to disable the response callback and http_req_failed tagging

When it happens

Trigger: Thrown at js/modules/k6/http/response_callback.go:91 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/077ac75a7d7e3314. Report an issue: GitHub.