grafana/k6 · error

%s

Error message

%s

What it means

The JavaScript that k6 evaluated inside the browser threw an exception. CDP returned exceptionDetails and k6 formats them (script, line, exception text) into this error. It is not a k6 failure: it is the page-side script failing — a syntax error in an evaluated string, a runtime error (undefined variable, null dereference), or an API call failing inside the page.

Source

Thrown at internal/js/modules/k6/browser/common/execution_context.go:224

	var (
		remoteObject     *runtime.RemoteObject
		exceptionDetails *runtime.ExceptionDetails
		err              error
	)
	if remoteObject, exceptionDetails, err = action.Do(cdp.WithExecutor(apiCtx, e.session)); err != nil {
		var cdpe *cdproto.Error
		if errors.As(err, &cdpe) && cdpe.Code == devToolsServerErrorCode {
			// By creating a new error instead of reusing it, we're removing the
			// chromium specific error code.
			return nil, errors.New(cdpe.Message)
		}

		e.logger.Debugf("ExecutionContext:eval", "Unexpected DevTools server error: %v", err)
		return nil, err
	}
	if exceptionDetails != nil {
		return nil, fmt.Errorf("%s", parseExceptionDetails(exceptionDetails))
	}
	var res any
	if remoteObject == nil {
		e.logger.Debugf(
			"ExecutionContext:eval",
			"sid:%s stid:%s fid:%s ectxid:%d furl:%q remoteObject is nil",
			e.sid, e.stid, e.fid, e.id, e.furl)
		return res, nil
	}

	if opts.returnByValue {
		res, err = valueFromRemoteObject(apiCtx, remoteObject)
		if err != nil {
			return nil, fmt.Errorf(
				"extracting value from remote object with ID %s: %w",
				remoteObject.ObjectID, err)
		}
	} else if remoteObject.ObjectID != "" {

View on GitHub (pinned to 93accf6570)

Solutions

1. Read the message: it contains the page exception text and location
2. Guard inside the evaluated script (null checks) or wait for the element first
3. Quote strings carefully when passing code as a string; prefer function form
4. If the page legitimately throws, catch it inside the evaluated code and return the error instead

Example fix

// before
await page.evaluate('document.querySelector("#x").click()');

// after
await page.click('#x'); // auto-waits for the element, or:
await page.evaluate('const el = document.querySelector("#x"); if (el) el.click();');

try {
  await page.evaluate(fn);
} catch (e) {
  // e.message carries the page-side exception; decide whether it is expected
  if (!/MyExpectedError/.test(e.message)) throw e;
}

When it happens

Trigger: page.evaluate('document.querySelector("#missing").click()') where the selector misses (TypeError on null); referencing variables that do not exist in the page context; syntax errors or unbalanced quotes in string-based evaluate calls; expected page errors such as JSON.parse of a failed fetch.

Common situations: Assuming selectors or globals exist without waiting; evaluating code copied from DevTools that depends on page globals; testing failure paths where the page itself throws; evaluating before the page's own scripts initialized.

Related errors

• evaluate requires a page function
• evaluating JS: %w
• k6/experimental/browser has been graduated, please use k6/br
• predicate function is not callable
• parsing new frame check options: %w

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/8b3c4828da649aae. Report an issue: GitHub.