grafana/k6 · error

setting emulated vision deficiency %q: %w

Error message

setting emulated vision deficiency %q: %w

What it means

After validating the vision deficiency name, Page.EmulateVisionDeficiency sends emulation.SetEmulatedVisionDeficiency over CDP; this error wraps a protocol-level failure of that command. Validation already passed, so the failure is environmental: detached session, closing page, or dead browser connection.

Source

Thrown at internal/js/modules/k6/browser/common/page.go:1105

func (p *Page) EmulateVisionDeficiency(typ string) error {
	p.logger.Debugf("Page:EmulateVisionDeficiency", "sid:%v typ:%s", p.sessionID(), typ)

	validTypes := map[string]emulation.SetEmulatedVisionDeficiencyType{
		"achromatopsia": emulation.SetEmulatedVisionDeficiencyTypeAchromatopsia,
		"blurredVision": emulation.SetEmulatedVisionDeficiencyTypeBlurredVision,
		"deuteranopia":  emulation.SetEmulatedVisionDeficiencyTypeDeuteranopia,
		"none":          emulation.SetEmulatedVisionDeficiencyTypeNone,
		"protanopia":    emulation.SetEmulatedVisionDeficiencyTypeProtanopia,
		"tritanopia":    emulation.SetEmulatedVisionDeficiencyTypeTritanopia,
	}
	t, ok := validTypes[typ]
	if !ok {
		return fmt.Errorf("unsupported vision deficiency: %s", typ)
	}

	action := emulation.SetEmulatedVisionDeficiency(t)
	if err := action.Do(cdp.WithExecutor(p.ctx, p.session)); err != nil {
		return fmt.Errorf("setting emulated vision deficiency %q: %w", typ, err)
	}

	applySlowMo(p.ctx)

	return nil
}

// Evaluate runs JS code within the execution context of the main frame of the page.
func (p *Page) Evaluate(pageFunc string, args ...any) (any, error) {
	p.logger.Debugf("Page:Evaluate", "sid:%v", p.sessionID())

	return p.MainFrame().Evaluate(pageFunc, args...)
}

// EvaluateHandle runs JS code within the execution context of the main frame of the page.
func (p *Page) EvaluateHandle(pageFunc string, args ...any) (JSHandleAPI, error) {
	p.logger.Debugf("Page:EvaluateHandle", "sid:%v", p.sessionID())

View on GitHub (pinned to 93accf6570)

Solutions

1. Verify the page is open and loaded before the call
2. Recreate the page if a crash was observed earlier
3. Move emulation earlier in the script, away from teardown
4. Check the browser process and websocket connection if it fails repeatedly

Example fix

// before
await page.close();
await page.emulateVisionDeficiency('deuteranopia');

// after
await page.emulateVisionDeficiency('deuteranopia');
await page.close();

if (page.isClosed()) throw new Error('page closed before vision emulation');

try { await page.emulateVisionDeficiency(typ); } catch (e) { if (!/setting emulated vision deficiency/.test(e.message)) throw e; }

When it happens

Trigger: page.emulateVisionDeficiency('none') on a page that is closing, whose renderer crashed, or after the DevTools connection dropped.

Common situations: Emulating vision deficiency near the end of an iteration while teardown begins; renderer crash from a heavy page; browser already closed by a prior statement.

Related errors

• internal error while initializing frame %T: %w
• internal error while updating emulated media: %w
• bringing page to front: %w
• emulating media: %w
• unsupported vision deficiency: %s

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/b608003d1cc050a9. Report an issue: GitHub.