<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>CSS Selectors Invalidation: :first-child :last-child</title>
    <link rel="help" href="https://drafts.csswg.org/selectors-4/#the-first-child-pseudo">
    <meta name="assert" content="This tests that the :first-child and :last-child selectors are effective">
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <style>
      div {
        color: black;
      }
      span:first-child {
        color: blue;
      }
      span:last-child {
        color: red;
      }
    </style>
  </head>
  <body>
    <div id="target"><span>first-initially</span><span>last-initially</span></div>
    <script>

'use strict';
const black = 'rgb(0, 0, 0)';
const blue = 'rgb(0, 0, 255)';
const red = 'rgb(255, 0, 0)';

test(() => {
  const target = document.querySelector('#target');
  const first = target.firstChild;
  assert_equals(getComputedStyle(first).color, blue);
  target.insertAdjacentHTML('afterbegin', '\n<span>foo</span><span>bar</span>');
  assert_equals(getComputedStyle(target.firstElementChild).color, blue);
  assert_equals(getComputedStyle(first).color, black);
  while (target.firstElementChild !== first)
    target.removeChild(target.firstElementChild);
  assert_equals(getComputedStyle(first).color, blue);
}, 'Adding multiple nodes at once should invalidate :first-child correctly.');

test(() => {
  const target = document.querySelector('#target');
  const last = target.lastChild;
  assert_equals(getComputedStyle(last).color, red);
  target.insertAdjacentHTML('beforeend', '\n<span>foo</span><span>bar</span>');
  assert_equals(getComputedStyle(target.lastChild).color, red);
  assert_equals(getComputedStyle(last).color, black);
  while (target.lastChild !== last)
    target.removeChild(target.lastChild);
  assert_equals(getComputedStyle(last).color, red);
}, 'Adding multiple nodes at once should invalidate :last-child correctly.');

    </script>
  </body>
</html>