<!DOCTYPE HTML> <meta charset=utf-8> <title>Layout Instability: observe after user input</title> <body> <style> #myDiv { position: relative; width: 300px; height: 100px; background: blue; } /* Disable the button's focus ring, which otherwise expands its visual rect by * 1px on all sides, triggering a layout shift event. */ #button { outline: none; } </style> <div id='myDiv'></div> <button id='button'>Generate a 'click' event</button> <script src=/resources/testharness.js></script> <script src=/resources/testharnessreport.js></script> <script src=/resources/testdriver.js></script> <script src=/resources/testdriver-vendor.js></script> <script src=resources/util.js></script> <script src=/event-timing/resources/event-timing-test-utils.js></script> <script> let timeAfterClick; 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 => { const observer = new PerformanceObserver( t.step_func(entryList => { const endTime = performance.now(); assert_equals(entryList.getEntries().length, 1); const entry = entryList.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)); // We should see that there was a click input entry. assert_equals(entry.hadRecentInput, true); assert_greater_than_equal(timeAfterClick, entry.lastInputTime); resolve(); }) ); observer.observe({entryTypes: ['layout-shift']}); // User input event clickAndBlockMain('button').then(() => { timeAfterClick = performance.now(); // Modify the position of the div. document.getElementById('myDiv').style = "top: 60px"; }); }); }, 'Layout shift right after user input is observable via PerformanceObserver.'); </script> </body>