grafana/k6 · error

adding web vital init script to new browser context: %w

Error message

adding web vital init script to new browser context: %w

What it means

Identical mechanism to the previous error but for the second injection: NewBrowserContext adds js.WebVitalInitScript (browser_context.go:154), the script that actually wires up web-vitals metric collection, on every existing page. Seeing this (rather than the IIFE one) means the first CDP injection succeeded and the sequence failed mid-way — most likely the connection or a page session died between the two calls.

Source

Thrown at internal/js/modules/k6/browser/common/browser_context.go:154

		browser:          browser,
		id:               id,
		opts:             opts,
		logger:           logger,
		timeoutSettings:  NewTimeoutSettings(nil),
	}

	if len(opts.Permissions) > 0 {
		err := b.GrantPermissions(opts.Permissions, GrantPermissionsOptions{})
		if err != nil {
			return nil, err
		}
	}

	if err := b.AddInitScript(js.WebVitalIIFEScript); err != nil {
		return nil, fmt.Errorf("adding web vital script to new browser context: %w", err)
	}
	if err := b.AddInitScript(js.WebVitalInitScript); err != nil {
		return nil, fmt.Errorf("adding web vital init script to new browser context: %w", err)
	}
	if err := b.setDownloadsPath(opts.DownloadsPath); err != nil {
		return nil, fmt.Errorf("setting downloads path: %w", err)
	}

	return &b, nil
}

// AddInitScript adds a script that will be initialized on all new pages.
func (b *BrowserContext) AddInitScript(script string) error {
	b.logger.Debugf("BrowserContext:AddInitScript", "bctxid:%v", b.id)

	b.evaluateOnNewDocumentSources = append(b.evaluateOnNewDocumentSources, script)

	for _, p := range b.browser.getPages() {
		if err := p.evaluateOnNewDocument(script); err != nil {
			return fmt.Errorf("adding init script to browser context: %w", err)
		}

View on GitHub (pinned to 93accf6570)

Solutions

1. Retry browser.newContext() after confirming the browser is still connected
2. Create contexts before any pages/popups exist so the per-page loop is trivial
3. Investigate chromium stability (OOM/shm) with K6_BROWSER_LOG=debug
4. Upgrade k6 for current web-vitals injection behavior

// same guard as the IIFE variant: create contexts early with zero open pages

try {
  ctx = browser.newContext()
} catch (e) {
  if (/adding web vital init script/.test(String(e))) {
    // mid-sequence connection loss; a fresh browser launch is needed
    throw e
  }
  throw e
}

When it happens

Trigger: The connection drops or a page session detaches exactly between the two addScriptToEvaluateOnNewDocument calls; chromium crashes during context creation while pages are open.

Common situations: Flaky chromium under memory pressure; creating contexts concurrently with page teardown; race with browser.close().

Related errors

• adding web vital script to new browser context: %w
• adding init script to browser context: %w
• adding k6 object to new browser context: %w
• connecting to Chromium over CDP: %w
• browser connect: %w

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/4acf8b8e15df94b7. Report an issue: GitHub.