progressively-loaded-image.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:
- /element-timing/progressively-loaded-image.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<html>

<meta charset=utf-8 />

<title>Element Timing: buffer elements before onload</title>

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

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

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

<body>

<script>

  let beforeRender;

  let img;

  // Number of characters to be read on the initial read, before sleeping.

  // Should be sufficient to do at least a first scan.

  let numInitial = 75;

  let sleep = 500;

  async_test(function(t) {

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

    const img_src = 'resources/progressive-image.py?name=square20.jpg&numInitial='

      + numInitial + '&sleep=' + sleep;

    const observer = new PerformanceObserver(

      t.step_func_done(function(entryList) {

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

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

        const pathname = window.location.origin + '/element-timing/' + img_src;

        // Since the image is only fully loaded after the sleep, the render timestamp

        // must be greater than |beforeRender| + |sleep|.

        checkElement(entry, pathname, 'my_image', '', beforeRender + sleep, img);

        checkNaturalSize(entry, 20, 20);

})

);

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

    img = document.createElement('img');

    img.src = img_src;

    img.setAttribute('elementtiming', 'my_image');

    document.body.appendChild(img);

    beforeRender = performance.now();

    t.step_timeout(() => {assert_true(0);}, 2000);

  }, "Element Timing: image render timestamp occurs after it is fully loaded.");

</script>