Blob.[arrayBuffer] promise's return is not an ArrayBuffer

Error message

Blob.[arrayBuffer] promise's return is not an ArrayBuffer

What it means

Error "Blob.[arrayBuffer] promise's return is not an ArrayBuffer" thrown in grafana/k6.

Source

Thrown at internal/js/modules/k6/websockets/helpers.go:61

func extractBytes(o *sobek.Object, rt *sobek.Runtime) []byte {
	arrayBuffer, ok := sobek.AssertFunction(o.Get("arrayBuffer"))
	if !ok {
		common.Throw(rt, errors.New("Blob.[arrayBuffer] is not a function"))
	}

	buffer, err := arrayBuffer(sobek.Undefined())
	if err != nil {
		common.Throw(rt, fmt.Errorf("call to Blob.[arrayBuffer] failed: %w", err))
	}

	p, ok := buffer.Export().(*sobek.Promise)
	if !ok {
		common.Throw(rt, errors.New("Blob.[arrayBuffer] return is not a Promise"))
	}

	ab, ok := p.Result().Export().(sobek.ArrayBuffer)
	if !ok {
		common.Throw(rt, errors.New("Blob.[arrayBuffer] promise's return is not an ArrayBuffer"))
	}

	return ab.Bytes()
}

View on GitHub (pinned to 93accf6570)

When it happens

Trigger: Thrown at internal/js/modules/k6/websockets/helpers.go:61 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/22feeeb4d16277c2. Report an issue: GitHub.