<!DOCTYPE HTML> <meta charset=utf-8> <title>Layout Instability entries are not available via the performance timeline</title> <body> <style> #myDiv { position: relative; width: 300px; height: 100px; background: blue; } </style> <div id='myDiv'></div> <script src="/resources/testharness.js"></script> <script src="/resources/testharnessreport.js"></script> <script src="resources/util.js"></script> <script> promise_test(async t => { assert_implements(window.LayoutShift, 'Layout Instability is not supported.'); // Wait for the initial render to complete. await waitForAnimationFrames(2); const startTime = performance.now(); return new Promise(resolve => { new PerformanceObserver(t.step_func(list => { const endTime = performance.now(); assert_equals(list.getEntries().length, 1); const entry = list.getEntries()[0]; assert_equals(entry.entryType, "layout-shift"); assert_equals(entry.name, ""); assert_greater_than_equal(entry.startTime, startTime); assert_less_than_equal(entry.startTime, endTime); assert_equals(entry.duration, 0.0); // The layout shift value should be: // 300 * (100 + 60) * (60 / maxDimension) / viewport size. assert_equals(entry.value, computeExpectedScore(300 * (100 + 60), 60)); // The entry should not be available via getEntries* methods. assert_equals(performance.getEntriesByType('layout-shift').length, 0, 'getEntriesByType should have no layout-shift entries'); assert_equals(performance.getEntriesByName('', 'layout-shift').length, 0, 'getEntriesByName should have no layout-shift entries'); assert_equals(performance.getEntries().filter(e => e.entryType === 'layout-shift').length, 0, 'getEntries should have no layout-shift entries'); resolve(); })).observe({type: 'layout-shift'}); // Modify the position of the div. document.getElementById('myDiv').style = "top: 60px"; }); }, 'Layout shift before onload is not buffered into the performance timeline.'); </script> </body>