shadowrootadoptedstylesheets-modulepreload-failure.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-modulepreload-failure.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<title>shadowrootadoptedstylesheets modulepreload failure</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">

  function preload(url) {

    const link = document.createElement("link");

    link.rel = "modulepreload";

    link.as = "style";

    link.href = url;

    const p = new Promise((resolve) => {

      link.onload = () => resolve("load");

      link.onerror = () => resolve("error");

});

    document.head.appendChild(link);

    return p;

  promise_test(async (t) => {

    // --- Scenario 1: modulepreload a nonexistent CSS file (404). ---

    const badUrl = "./support/nonexistent.css?modulepreload-failure";

    const result = await preload(badUrl);

    assert_equals(result, "error",

      "Preloading a 404 URL should fire the error event.");

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

    // A failed CSS module fetch should not contribute an entry.

    assert_equals(shadowRoot.adoptedStyleSheets.length, 0,

      "After failed preload: no sheet should be added.");

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

      "No styles should be applied from a failed modulepreload.");

  }, "Failed modulepreload (404) is skipped by shadowrootadoptedstylesheets.");

  promise_test(async (t) => {

    // --- Scenario 2: mix of valid and invalid modulepreloads. ---

    const badUrl2 = "./support/nonexistent-2.css?modulepreload-failure";

    const goodUrl = "./support/styles.css?modulepreload-failure";

    const [badResult, goodResult] =

      await Promise.all([preload(badUrl2), preload(goodUrl)]);

    assert_equals(badResult, "error", "Bad URL should fire error.");

    assert_equals(goodResult, "load", "Good URL should fire load.");

    const { shadowRoot: sr2, testElement: te2 } = createStylesheetHost(

      [badUrl2, goodUrl]);

    assert_equals(sr2.adoptedStyleSheets.length, 1,

      "Only the valid preload should contribute a sheet.");

    assertSheetRule(sr2, 0, "span { color: blue; }", "Valid preload");

    assert_equals(getComputedStyle(te2).color, "rgb(0, 0, 255)",

      "Blue styles from the valid preload should be applied.");

  }, "Mixed valid/invalid modulepreloads: failed ones are skipped and valid ones work.");

</script>

</body>