microsoft/playwright · error · Error

"nth-match" engine expects non-empty selector list and an in

Error message

"nth-match" engine expects non-empty selector list and an index argument

What it means

Error ""nth-match" engine expects non-empty selector list and an index argument" thrown in microsoft/playwright.

Source

Thrown at packages/injected/src/selectorEvaluator.ts:529

      const maxDistance = args.length && typeof args[args.length - 1] === 'number' ? args[args.length - 1] : undefined;
      const queryArgs = maxDistance === undefined ? args : args.slice(0, args.length - 1);
      if (args.length < 1 + (maxDistance === undefined ? 0 : 1))
        throw new Error(`"${name}" engine expects a selector list and optional maximum distance in pixels`);
      const inner = evaluator.query(context, queryArgs);
      const score = layoutSelectorScore(name, element, inner, maxDistance);
      if (score === undefined)
        return false;
      (evaluator as SelectorEvaluatorImpl)._markScore(element, score);
      return true;
    }
  };
}

const nthMatchEngine: SelectorEngine = {
  query(context: QueryContext, args: (string | number | Selector)[], evaluator: SelectorEvaluator): Element[] {
    let index = args[args.length - 1];
    if (args.length < 2)
      throw new Error(`"nth-match" engine expects non-empty selector list and an index argument`);
    if (typeof index !== 'number' || index < 1)
      throw new Error(`"nth-match" engine expects a one-based index as the last argument`);
    const elements = isEngine.query!(context, args.slice(0, args.length - 1), evaluator);
    index--;  // one-based
    return index < elements.length ? [elements[index]] : [];
  },
};

function parentElementOrShadowHostInContext(element: Element, context: QueryContext): Element | undefined {
  if (element === context.scope)
    return;
  if (!context.pierceShadow)
    return element.parentElement || undefined;
  return parentElementOrShadowHost(element);
}

function previousSiblingInContext(element: Element, context: QueryContext): Element | undefined {
  if (element === context.scope)

View on GitHub (pinned to c8fc3bf8d3)

When it happens

Trigger: Thrown at packages/injected/src/selectorEvaluator.ts:529 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/playwright@c8fc3bf8d3 (2026-08-12). Data as JSON: /api/errors/4ad6115f3a47747b. Report an issue: GitHub.