containertiming-img-already-loaded.html

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This WPT test may be referenced by the following Test IDs:
- /container-timing/tentative/containertiming-img-already-loaded.html - WPT Dashboard Interop Dashboard

<!DOCTYPE HTML>

<meta charset=utf-8>

<title>Container Timing: observe an image whose resource is already loaded</title>

<body>

<style>

body {

  margin: 0;

</style>

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

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

<script src="/container-timing/resources/container-timing-helpers.js"></script>

<script>

  // Like containertiming-img-itself.html, but the resource is fully loaded

  // before the <img> is inserted, so the load is notified for an element that

  // has never been laid out. Happens naturally when the image is cached.

  const IMAGE_URL = '/container-timing/resources/square100.png';

  let beforeRender;

  async_test(function (t) {

    assert_implements(window.PerformanceContainerTiming, "PerformanceContainerTiming is not implemented");

    const observer = new PerformanceObserver(

      t.step_func_done(function(entryList) {

        assert_equals(entryList.getEntries().length, 1);

        const entry = entryList.getEntries()[0];

        checkContainerEntry(entry, 'image_ct', 'my_id', beforeRender);

})

);

    observer.observe({entryTypes: ['container']});

    const preload = new Image();

    preload.onload = t.step_func(function() {

      const img = document.createElement('img');

      img.src = IMAGE_URL;

      img.setAttribute('containertiming', 'image_ct');

      img.setAttribute('id', 'my_id');

      document.body.appendChild(img);

      beforeRender = performance.now();

});

    preload.src = IMAGE_URL;

  }, 'An already-loaded image with containertiming still reports its paint.');

</script>

</body>