shadowrootadoptedstylesheets-async-fetch.html

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This test has a WPT meta file that expects 1 subtest issues.
This WPT test may be referenced by the following Test IDs:
- /shadow-dom/declarative/tentative/shadowrootadoptedstylesheets/shadowrootadoptedstylesheets-async-fetch.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<title>shadowrootadoptedstylesheets async fetch</title>

<meta name="author" title="Kurt Catti-Schmidt" href="mailto:kschmi@microsoft.com" />

<link rel='help' href='https://github.com/whatwg/html/pull/11687'>

<script src='/resources/testharness.js'></script>

<script src='/resources/testharnessreport.js'></script>

<script src='./support/helpers.js'></script>

<body>

<script type="module">

  promise_test(async (t) => {

    // Create a shadow root that references a CSS module specifier that hasn't

    // been fetched yet. An empty placeholder sheet should be added to

    // adoptedStyleSheets immediately, and populated when the fetch completes.

    const cssUrl = "./support/styles.css?async_fetch";

    const { shadowRoot, testElement } = createStylesheetHost(cssUrl);

    assert_equals(shadowRoot.adoptedStyleSheets.length, 1,

      "Before fetch: expected 1 placeholder(s).");

    assert_equals(shadowRoot.adoptedStyleSheets[0].cssRules.length, 0,

      "Before fetch: placeholder at index 0 should be empty.");

    assert_equals(getComputedStyle(testElement).color, "rgb(0, 0, 0)",

      "Styles should not yet be applied from the empty placeholder.");

    await fetchAndWait(cssUrl);

    assertSheetRule(shadowRoot, 0, "span { color: blue; }", "After fetch");

    assert_equals(getComputedStyle(testElement).color, "rgb(0, 0, 255)",

      "Styles were applied after async fetch.");

  }, "Async-fetched CSS module replaces placeholder and applies styles.");

</script>

</body>