grafana/k6 · error

adding init script to browser context: %w

Error message

adding init script to browser context: %w

What it means

browserContext.addInitScript(script) records the script for future pages and immediately injects it into every currently open page (browser_context.go:171). If any page's CDP Page.addScriptToEvaluateOnNewDocument call fails, the whole operation errors with this wrap naming the init-script step.

Source

Thrown at internal/js/modules/k6/browser/common/browser_context.go:171

	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)
		}
	}

	return nil
}

func (b *BrowserContext) applyAllInitScripts(p *Page) error {
	for _, source := range b.evaluateOnNewDocumentSources {
		if err := p.evaluateOnNewDocument(source); err != nil {
			return fmt.Errorf("adding init script to browser context: %w", err)
		}
	}

	return nil
}

// Browser returns the browser instance that this browser context belongs to.
func (b *BrowserContext) Browser() *Browser {

View on GitHub (pinned to 93accf6570)

Solutions

1. Call addInitScript immediately after newContext(), before any pages exist, so the per-page loop is empty
2. Close/remove crashed pages before adding scripts; the wrapped error identifies the failing page
3. Minify or split very large init scripts
4. Recreate the context if the wrapped error shows the connection is dead

Example fix

// before
const page = ctx.newPage()
await page.goto('https://example.com')
ctx.addInitScript('window.token = "x"') // injects into live pages, can fail

// after
const ctx = browser.newContext()
ctx.addInitScript('window.token = "x"') // no pages yet — safe
const page = ctx.newPage()

// register init scripts before any page exists
const ctx = browser.newContext()
ctx.addInitScript('window.bootstrap = true') // no pages yet — cannot fail per-page
const page = ctx.newPage()

try {
  ctx.addInitScript(script)
} catch (e) {
  if (/adding init script/.test(String(e))) {
    // a live page's session failed; recreate the context for a clean slate
    throw e
  }
  throw e
}

When it happens

Trigger: Calling addInitScript after one of the open pages crashed or its session closed at the CDP level; connection lost mid-loop over pages; extremely large script payloads troubling the websocket transport.

Common situations: Injecting auth/bootstrap scripts after navigation has started; races between page.close() and addInitScript(); injecting big bundled JS as an init script.

Related errors

• adding web vital script to new browser context: %w
• adding web vital init script to new browser context: %w
• adding k6 object to new browser context: %w
• browser connect: %w
• disposing browser context ID %s: %w

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/f50c2c70cba8abb8. Report an issue: GitHub.