web-font-styled-text-resize-swap-after-interaction.html

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This WPT test may be referenced by the following Test IDs:
- /largest-contentful-paint/web-font-styled-text-resize-swap-after-interaction.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

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

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

<script src=/resources/testdriver.js></script>

<script src=/resources/testdriver-actions.js></script>

<script src=/resources/testdriver-vendor.js></script>

<style></style>

<!--

  Web-font styled text that gets resized after an interaction stops LCP

  observation should not make a new LCP emission.

-->

<textarea id='input'></textarea>

<div class="test">LCP: Web Font Styled Text Resize</div>

<script>

  function addCSSRules() {

    styleSheet = document.styleSheets[0];

    fontRuleSet = "@font-face {\

      font-family: 'ADTestFaceInteraction';\

      src: url('/fonts/AD.woff');\

      font-display: swap;\

}";

    fontAtRule = ".test {\

      font-family: 'ADTestFaceInteraction';\

    } ";

    styleSheet.insertRule(fontRuleSet);

    styleSheet.insertRule(fontAtRule);

  function LCPEntryList(t) {

    return new Promise(resolve => {

      let = lcpEntries = [];

      new PerformanceObserver((entryList, observer) => {

        lcpEntries = lcpEntries.concat(entryList.getEntries());

        if (lcpEntries) {

          // Adding timeout to wait a bit more so that if there are more than

          // expected LCP entries emitted, they can be observed.

          t.step_timeout(() => {

            resolve(lcpEntries);

            observer.disconnect();

          }, 200);

      }).observe({ type: 'largest-contentful-paint', buffered: true });

});

  promise_test(async t => {

    await document.fonts.ready;

    let system_font_size = document.getElementsByClassName('test')[0].offsetHeight;

    // Verify an LCP entry is emitted.

    let entryList = await LCPEntryList(t);

    assert_equals(entryList.length, 1, 'Text with system font should make a LCP emission.');

    let lcpEntryBeforeInteraction = entryList[0];

    // Add event listener so that CSS rule would be added after there's an

    // input.

    let inputElement = document.getElementById('input');

    inputElement.addEventListener('keydown', addCSSRules);

    // Send key as input.

    await test_driver.send_keys(inputElement, 'k');

    // Wait for web font to load.

    await document.fonts.ready;

    // Verify web font is downloaded.

    assert_own_property(window, 'PerformanceResourceTiming', "ResourceTiming not supported");

    let url = '/fonts/AD.woff';

    var absoluteURL = new URL(url, location.href).href;

    assert_equals(performance.getEntriesByName(absoluteURL).length, 1, 'Web font should be downloaded.');

    // Verify web font is available.

    assert_true(document.fonts.check('16px ADTestFaceInteraction'), 'Font should be the web font added');

    // Verify web font is applied.

    let web_font_size = document.getElementsByClassName('test')[0].offsetHeight;

    assert_not_equals(web_font_size, system_font_size, 'Web font swap should happen');

    // Assert there is only 1 LCP entry, which verifies the added web font does

    // not make a new LCP entry after an input.

    entryList = await LCPEntryList(t);

    assert_equals(entryList.length, 1, 'Text with system font should not make a LCP emission.');

    // Verify the LCP entry is the same one emitted before interaction by

    // asserting the size is the same.

    assert_equals(lcpEntryBeforeInteraction.size, entryList[0].size, 'There should be only 1 LCP entry emitted.');

  }, "LCP should be not updated if the web font styled text resize occurs after an interaction happens");

</script>