grafana/k6 · error

couldn't get ArrayBuffer.isView as it isn't a function

Error message

couldn't get ArrayBuffer.isView as it isn't a function

What it means

Environment guard in the ArrayBufferView detection helper: isArrayBufferView looks up ArrayBuffer.isView in the current Sobek runtime and asserts it is callable. This sentinel error is returned when the property exists but is not a function (or is missing), meaning the script's global environment has been modified — a polyfill, mock, or accidental assignment has clobbered the built-in ArrayBuffer.isView.

Source

Thrown at internal/js/modules/k6/websockets/websockets.go:724

		mtype: websocket.BinaryMessage,
		data:  b,
		t:     time.Now(),
	}
}

func isArrayBufferView(rt *sobek.Runtime, v sobek.Value) (bool, error) {
	var isView sobek.Callable
	var ok bool
	exc := rt.Try(func() {
		isView, ok = sobek.AssertFunction(
			rt.Get("ArrayBuffer").ToObject(rt).Get("isView"))
	})
	if exc != nil {
		return false, exc
	}

	if !ok {
		return false, fmt.Errorf("couldn't get ArrayBuffer.isView as it isn't a function")
	}

	boolValue, err := isView(nil, v)
	if err != nil {
		return false, err
	}
	return boolValue.ToBoolean(), nil
}

// Ping sends a ping message over the websocket.
func (w *webSocket) ping() {
	w.assertStateOpen()

	pingID := strconv.Itoa(w.sendPings.counter)

	w.writeQueueCh <- message{
		mtype: websocket.PingMessage,
		data:  []byte(pingID),

View on GitHub (pinned to 165bb3c1a4)

Solutions

1. Remove any script code that reassigns ArrayBuffer.isView or the ArrayBuffer global
2. Disable libraries or shims that replace standard built-ins
3. Send strings or Blobs instead of typed arrays to avoid the isView lookup entirely

When it happens

Trigger: Thrown at internal/js/modules/k6/websockets/websockets.go:699 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@165bb3c1a4 (2026-08-18). Data as JSON: /api/errors/6c8a49a6324a07fc. Report an issue: GitHub.