| <!DOCTYPE HTML> |
| <meta charset=utf-8> |
| <title>Layout Jank: observe jank fraction via PerformanceObserver</title> |
| <body> |
| <style> |
| #myDiv { position: relative; width: 300px; height: 100px; } |
| </style> |
| <div id='myDiv'></div> |
| <script src="/resources/testharness.js"></script> |
| <script src="/resources/testharnessreport.js"></script> |
| <script> |
| async_test(function (t) { |
| const observer = new PerformanceObserver( |
| t.step_func_done(function(entryList) { |
| assert_equals(entryList.getEntries().length, 1); |
| const entry = entryList.getEntries()[0]; |
| assert_equals(entry.entryType, "layoutJank"); |
| assert_equals(entry.name, ""); |
| assert_equals(entry.startTime, 0.0); |
| assert_equals(entry.duration, 0.0); |
| // The layout jank fraction should be: 300 * (100 + 60) / viewport size. |
| assert_equals(entry.fraction, 300 * (100 + 60) / |
| (document.documentElement.clientWidth * document.documentElement.clientHeight)); |
| }) |
| ); |
| observer.observe({entryTypes: ['layoutJank']}); |
| window.onload = () => { |
| // Modify the position of the div. |
| document.getElementById('myDiv').style = "top: 60px"; |
| }; |
| }, 'LayoutJank is observable via PerformanceObserver.'); |
| </script> |
| |
| </body> |
