`k6/html`: `Tester` callback (filter/is/not) is typed with `Element` but k6 passes a `Selection`

[TheOneFromNorway]

Brief summary

The Tester interface is the callback type for Selection.filter(), Selection.is() and Selection.not(). It declares the second parameter as an Element:

export interface Tester {
    (index: number, element: Element): boolean;
}

At runtime, however, k6/html invokes these callbacks with a Selection, not an Element. Because Selection does not expose Element-only members such as querySelector, code that type-checks against these definitions throws at runtime:

TypeError: Object has no member 'querySelector'

k6 version

v2.0.0

OS

all

Docker version and image (if applicable)

No response

Steps to reproduce the problem

With test plan

import { parseHTML } from 'k6/html';

export default function () {
  const doc = parseHTML('<div class="c"><a href="/x">John</a></div>');

  doc.find('div.c').filter((_i, el) => el.querySelector('a[href]') != null);
}

you already see the issue. The code compiles cleanly (TS thinks el is an Element, which has querySelector) but throws at runtime because el is actually a Selection and you get
TypeError: Object has no member 'querySelector'

Why this is a type bug (not version-specific)

• The official Selection.filter() documentation example uses el.text() — a Selection method — inside the callback:
  https://grafana.com/docs/k6/latest/javascript-api/k6-html/selection/selection-filter/
• The definitions are internally inconsistent: Mapper (the Selection.map() callback, which also receives a Selection) is already correctly typed with Selection, while Tester is not.
• Reproduces identically on k6 v1.3.0 and v2.0.0, so it is independent of the k6 binary version.

Expected behaviour

Type Tester callback's second parameter as a Selection:

export interface Tester {
    (index: number, selection: Selection): boolean;
}

Actual behaviour

Type the Tester callback's second parameter is typed as an Element even though it is not