larger-text.html (3453B)
1 <!DOCTYPE HTML> 2 <meta charset=utf-8> 3 <title>Largest Contentful Paint: largest text is reported.</title> 4 5 <body> 6 <script src="/resources/testharness.js"></script> 7 <script src="/resources/testharnessreport.js"></script> 8 <style type="text/css"> 9 #text2 { 10 position: absolute; 11 width: auto; 12 white-space: nowrap; 13 } 14 15 </style> 16 <!-- These are some text and some tiny images. We care about the largest text. --> 17 <img id='image1' /> 18 <div id='text1'></div> 19 <div id='text2'></div> 20 <img id='image2' /> 21 <script> 22 const load_image = async (id, url) => { 23 await new Promise(resolve => { 24 const image = document.getElementById(id); 25 image.addEventListener('load', resolve); 26 image.src = url; 27 }); 28 } 29 30 const load_text = (id, text) => { 31 let div = document.getElementById(id); 32 div.innerHTML = text; 33 } 34 35 promise_test(async (t) => { 36 assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented"); 37 let beforeRender = performance.now(); 38 39 // Load images and add texts. 40 await load_image('image1', '/images/lcp-1x1.png'); 41 42 load_text('text1', 'This is some text.'); 43 44 load_text('text2', 'This is more text so it will be the Largest Contentful Paint!'); 45 46 await load_image('image2', '/images/lcp-2x2.png'); 47 48 await new Promise(resolve => { 49 new PerformanceObserver( 50 (entryList, observer) => { 51 entryList.getEntries().forEach(entry => { 52 // The tiny images or text1 could be reported as LCP if it is rendered before text2. 53 if (entry.id !== 'text2') 54 return; 55 56 assert_equals(entry.entryType, 'largest-contentful-paint', 57 'The entry entryType should be largest-contentful-paint.'); 58 59 assert_greater_than_equal(entry.renderTime, beforeRender, 60 'The entry renderTime should be greater than or equal to the beforeRender.'); 61 62 assert_greater_than_equal(performance.now(), entry.renderTime, 63 'The performance.now() timestamp should be greater than or equal to the entry renderTime.'); 64 65 assert_approx_equals(entry.startTime, entry.renderTime, 0.001, 66 'The entry startTime should be equal to renderTime to the precision of 1 millisecond.'); 67 68 assert_equals(entry.duration, 0, 'The entry duration should be 0.'); 69 70 const div = document.getElementById('text2'); 71 72 // The div styling makes it approximate the text size. 73 assert_greater_than_equal(entry.size, (div.clientHeight - 5) * (div.clientWidth - 5), 74 'Reported LCP size should not be significantly smaller than the text2 div.'); 75 76 assert_less_than_equal(entry.size, (div.clientHeight + 1) * (div.clientWidth + 1), 77 'Reported LCP size should not be larger than the text2 div.'); 78 79 assert_equals(entry.loadTime, 0, 'The entry loadTime should be 0.'); 80 81 assert_equals(entry.url, '', 'The entry url should be empty.'); 82 83 assert_equals(entry.element, div, 'The entry element should be test2 div.'); 84 85 observer.disconnect(); 86 87 resolve(); 88 }) 89 }).observe({ type: 'largest-contentful-paint', buffered: true }); 90 }); 91 }, 'Largest Contentful Paint: largest text is reported.'); 92 </script> 93 </body>