testing/web-platform/tests/element-timing/observe-elementtiming.html

   1 <!DOCTYPE HTML>
   2 <meta charset=utf-8>
   3 <title>Element Timing: observe elements with elementtiming attribute</title>
   4 <body>
   5 <style>
   6 body {
   7   margin: 0;
   8 }
   9 </style>
  10 <script src="/resources/testharness.js"></script>
  11 <script src="/resources/testharnessreport.js"></script>
  12 <script src="resources/element-timing-helpers.js"></script>
  13 <script>
  14   let beforeRender;
  15   let img;
  16   async_test(function (t) {
  17     if (!window.PerformanceElementTiming) {
  18       assert_unreached("PerformanceElementTiming is not implemented");
  19     }
  20     const observer = new PerformanceObserver(
  21       t.step_func_done(function(entryList) {
  22         assert_equals(entryList.getEntries().length, 1);
  23         const entry = entryList.getEntries()[0];
  24         const pathname = window.location.origin + '/element-timing/resources/square100.png';
  25         checkElement(entry, pathname, 'my_image', 'my_id', beforeRender, img);
  26         // Assume viewport has size at least 100, so the element is fully visible.
  27         checkRect(entry, [0, 100, 0, 100]);
  28         checkNaturalSize(entry, 100, 100);
  29       })
  30     );
  31     observer.observe({entryTypes: ['element']});
  32     // We add the image during onload to be sure that the observer is registered
  33     // in time for it to observe the element timing.
  34     window.onload = () => {
  35       // Add image of width equal to 100 and height equal to 100.
  36       img = document.createElement('img');
  37       img.src = 'resources/square100.png';
  38       img.setAttribute('elementtiming', 'my_image');
  39       img.setAttribute('id', 'my_id');
  40       document.body.appendChild(img);
  41       beforeRender = performance.now();
  42     };
  43   }, 'Element with elementtiming attribute is observable.');
  44 </script>
  45
  46 </body>