grafana/k6 · error

setting window bounds: %w

Error message

setting window bounds: %w

What it means

Only in headed mode (hasUIWindow), after viewport emulation k6 resizes the actual OS window with Browser.setWindowBounds so the visible window matches the emulated viewport plus OS-specific insets. This error means that window-resize command failed. In headless mode this code path is skipped entirely.

Source

Thrown at internal/js/modules/k6/browser/common/frame_session.go:1272

		WithScreenWidth(screen.Width).
		WithScreenHeight(screen.Height)
	if err := action.Do(cdp.WithExecutor(fs.ctx, fs.session)); err != nil {
		return fmt.Errorf("emulating viewport: %w", err)
	}

	if fs.hasUIWindow {
		// add an inset to viewport depending on the operating system.
		// this won't add an inset if we're running in headless mode.
		viewport = viewport.recalculateInset(
			fs.page.browserCtx.browser.browserOpts.Headless,
			runtime.GOOS,
		)
		action2 := browser.SetWindowBounds(fs.windowID, &browser.Bounds{
			Width:  viewport.Width,
			Height: viewport.Height,
		})
		if err := action2.Do(cdp.WithExecutor(fs.ctx, fs.session)); err != nil {
			return fmt.Errorf("setting window bounds: %w", err)
		}
	}

	return nil
}

func (fs *FrameSession) executionContextForID(
	executionContextID cdpruntime.ExecutionContextID,
) (*ExecutionContext, error) {
	fs.contextIDToContextMu.Lock()
	defer fs.contextIDToContextMu.Unlock()

	if exc, ok := fs.contextIDToContext[executionContextID]; ok {
		return exc, nil
	}

	return nil, fmt.Errorf("no execution context found for id: %v", executionContextID)
}

View on GitHub (pinned to 93accf6570)

Solutions

1. Run headless in CI, or provide a real display/xvfb when headed mode is required
2. Do not close or minimize the window between page creation and viewport application
3. Retry once; if the emulated viewport already applied, the window bounds step is cosmetic and a retry usually succeeds
4. Upgrade k6: window bounds and inset handling have improved across releases

Example fix

// before: headed CI without display
const browser = chromium.launch({ headless: false });
const page = await browser.newPage({ viewport: { width: 1280, height: 720 } });

// after: headless for CI
const browser = chromium.launch({ headless: true });
const page = await browser.newPage({ viewport: { width: 1280, height: 720 } });

// avoid the headed window-resize path entirely in CI
const headless = __ENV.CI === 'true';
const browser = chromium.launch({ headless });

try { await page.setViewport(...); }
catch (e) { if (!/setting window bounds/.test(String(e.message))) throw e; /* retry or continue */ }

When it happens

Trigger: Running with headless: false together with a viewport option; the window ID became invalid (window closed between page creation and resize), the window is minimized/fullscreen so it cannot be resized, or the DevTools connection dropped before the command was executed.

Common situations: Local headed debugging with an explicit viewport; CI jobs accidentally running headed without a display server or window manager; desktop environments denying programmatic resize; closing the window manually mid-test.

Related errors

• emulating viewport: %w
• WebSocket endpoint cannot be empty
• can't fetch the page for unknown reason
• errorText
• parent frame has been detached

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/838608cf0152f625. Report an issue: GitHub.