adding web vital script to new browser context

Error message

adding web vital script to new browser context: %w

What it means

Every new BrowserContext registers a web-vitals IIFE script via AddInitScript, which also injects it into every already-open page of the browser with Page.addScriptToEvaluateOnNewDocument. This error wraps a failure of that registration when creating the context. It cannot come from the script content (which is a constant) — it comes from the CDP calls against existing pages failing.

Solutions

Create all browser contexts before heavy page churn, and avoid newContext() during teardown
Retry creating the context once after closing or stabilizing broken pages
Use K6_BROWSER_LOG=debug to see which existing page rejected the injection
Upgrade k6 — web-vital script registration has seen fixes across releases

Example fix

// before
const ctx2 = browser.newContext(); // while a page in ctx1 is crashing/closing

// after
await brokenPage.close(); // stabilize first
const ctx2 = browser.newContext();

Defensive patterns

Strategy: retry

Validate before calling

// Create contexts before page churn begins
export function setup() {
  // contexts created once, up front — not mid-run while pages crash
}

Try / catch

try {
  ctx = browser.newContext();
} catch (e) {
  if (String(e).includes('adding web vital script')) {
    // an existing page's session rejected injection; close broken pages and retry
    for (const p of browser.contexts().pages()) { /* close unusable pages */ }
    ctx = browser.newContext();
  } else throw e;
}

Prevention

Create all browser contexts early, before heavy navigation workloads
Avoid newContext() during teardown
Close crashed pages instead of leaving them attached

When it happens

Trigger: Calling browser.newContext() while existing pages are in a bad state (crashed target, closed session) so evaluateOnNewDocument fails; creating a context as the browser/connection is shutting down.

Common situations: Opening new contexts after some pages crashed mid-run; creating contexts during teardown while k6 closes the browser; heavily loaded browsers whose page targets die concurrently.

Related errors

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/239291e39047a66b. Report an issue: GitHub.

Appendix: 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() {

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