buffered-flag.window.js

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This WPT test may be referenced by the following Test IDs:
- /paint-timing/fcp-only/buffered-flag.window.html - WPT Dashboard Interop Dashboard

setup({"hide_test_state": true});

async_test(t => {

  assert_implements(window.PerformancePaintTiming, "Paint Timing isn't supported.");

  // First observer creates a second one in the callback to ensure the entry has been dispatched

  // by the time the second observer begins observing.

  new PerformanceObserver(entries => {

    const entry_seen = entries.getEntriesByName('first-contentful-paint').length > 0;

    // Abort if we have not yet received the entry.

    if (!entry_seen)

      return;

    // Second observer requires 'buffered: true' to see the entry.

    new PerformanceObserver(t.step_func_done(list => {

        const fcp = list.getEntriesByName('first-contentful-paint');

        assert_equals(fcp.length, 1, 'Should have an fcp entry');

        const entry = fcp[0];

        assert_equals(entry.entryType, 'paint');

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

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

  // Trigger the first contentful paint entry.

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

  img.src = "../resources/circles.png";

  document.body.appendChild(img);

}, "PerformanceObserver with buffered flag sees previous FCP entry.");