grafana/k6 · error

adding web vital script to new browser context: %w

Error message

adding web vital script to new browser context: %w

What it means

Creating a browser context registers k6's web-vitals collection scripts on every already-existing page via CDP Page.addScriptToEvaluateOnNewDocument (browser_context.go:151). This is the first of two injections (the WebVitalIIFEScript bootstrap); if the CDP round-trip fails on any existing page, NewBrowserContext aborts with this wrap.

Source

Thrown at internal/js/modules/k6/browser/common/browser_context.go:151

	b := BrowserContext{
		BaseEventEmitter: NewBaseEventEmitter(ctx),
		ctx:              ctx,
		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() {

View on GitHub (pinned to 93accf6570)

Solutions

1. Read the wrapped CDP error — connection errors mean chromium died; confirm with K6_BROWSER_LOG=debug
2. Create all contexts early, before heavy navigation/load
3. Add resources (memory, --shm-size) or reduce VUs if chromium is OOM-killed
4. Upgrade k6; init-script injection and crash handling improved across releases

// create all contexts early in the iteration, before load/navigation
// const ctx = browser.newContext() — do it right after launch

try {
  ctx = browser.newContext()
} catch (e) {
  if (/adding web vital script/.test(String(e)) && /connection|closed/i.test(String(e))) {
    throw e // chromium died — restarting requires a new browser
  }
  throw e
}

When it happens

Trigger: browser.newContext() issued while the CDP connection is dropping or chromium just crashed; an existing page's session already detached; browser.close() racing newContext().

Common situations: Under-resourced chromium dying mid-test (OOM, no shm); calling newContext() after the browser disconnected; creating contexts late in the iteration near teardown.

Related errors

• adding web vital init 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/239291e39047a66b. Report an issue: GitHub.