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<title>[56399] trunk/tests/performance: Build/Test Tools: Measure additional load time metrics in performance tests.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/56399">56399</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/56399","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>swissspidy</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2023-08-16 08:46:22 +0000 (Wed, 16 Aug 2023)</dd>
</dl>
<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>Build/Test Tools: Measure additional load time metrics in performance tests.
Three new metrics are being collected and reported as part of this change:
- Time To First Byte (TTFB) - the time between the request for a resource and when the first byte of a response begins to arrive
- Largest Contentful Paint (LCP) - the render time of the largest image or text block visible within the viewport
- The difference between the two (LCP minus TTFB)
Props joemcgill, flixos90, oandregal, mukesh27, youknowriad, swissspidy.
Fixes <a href="https://core.trac.wordpress.org/ticket/58360">#58360</a>.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunktestsperformancespecshomeblockthemetestjs">trunk/tests/performance/specs/home-block-theme.test.js</a></li>
<li><a href="#trunktestsperformancespecshomeclassicthemetestjs">trunk/tests/performance/specs/home-classic-theme.test.js</a></li>
<li><a href="#trunktestsperformanceutilsjs">trunk/tests/performance/utils.js</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunktestsperformancespecshomeblockthemetestjs"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/tests/performance/specs/home-block-theme.test.js</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/tests/performance/specs/home-block-theme.test.js 2023-08-16 00:13:45 UTC (rev 56398)
+++ trunk/tests/performance/specs/home-block-theme.test.js 2023-08-16 08:46:22 UTC (rev 56399)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -3,7 +3,11 @@
</span><span class="cx" style="display: block; padding: 0 10px"> */
</span><span class="cx" style="display: block; padding: 0 10px"> const { basename, join } = require( 'path' );
</span><span class="cx" style="display: block; padding: 0 10px"> const { writeFileSync } = require( 'fs' );
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-const { getResultsFilename } = require( './../utils' );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+const {
+ getResultsFilename,
+ getTimeToFirstByte,
+ getLargestContentfulPaint,
+} = require( './../utils' );
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span><span class="cx" style="display: block; padding: 0 10px"> * WordPress dependencies.
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -15,6 +19,9 @@
</span><span class="cx" style="display: block; padding: 0 10px"> wpBeforeTemplate: [],
</span><span class="cx" style="display: block; padding: 0 10px"> wpTemplate: [],
</span><span class="cx" style="display: block; padding: 0 10px"> wpTotal: [],
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ timeToFirstByte: [],
+ largestContentfulPaint: [],
+ lcpMinusTtfb: [],
</ins><span class="cx" style="display: block; padding: 0 10px"> };
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> beforeAll( async () => {
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -22,7 +29,9 @@
</span><span class="cx" style="display: block; padding: 0 10px"> } );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> afterAll( async () => {
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- const resultsFilename = getResultsFilename( basename( __filename, '.js' ) );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ const resultsFilename = getResultsFilename(
+ basename( __filename, '.js' )
+ );
</ins><span class="cx" style="display: block; padding: 0 10px"> writeFileSync(
</span><span class="cx" style="display: block; padding: 0 10px"> join( __dirname, resultsFilename ),
</span><span class="cx" style="display: block; padding: 0 10px"> JSON.stringify( results, null, 2 )
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -40,14 +49,19 @@
</span><span class="cx" style="display: block; padding: 0 10px"> const [ navigationTiming ] = JSON.parse( navigationTimingJson );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> results.wpBeforeTemplate.push(
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- navigationTiming.serverTiming[0].duration
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ navigationTiming.serverTiming[ 0 ].duration
</ins><span class="cx" style="display: block; padding: 0 10px"> );
</span><span class="cx" style="display: block; padding: 0 10px"> results.wpTemplate.push(
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- navigationTiming.serverTiming[1].duration
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ navigationTiming.serverTiming[ 1 ].duration
</ins><span class="cx" style="display: block; padding: 0 10px"> );
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- results.wpTotal.push(
- navigationTiming.serverTiming[2].duration
- );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ results.wpTotal.push( navigationTiming.serverTiming[ 2 ].duration );
+
+ const ttfb = await getTimeToFirstByte();
+ const lcp = await getLargestContentfulPaint();
+
+ results.timeToFirstByte.push( ttfb );
+ results.largestContentfulPaint.push( lcp );
+ results.lcpMinusTtfb.push( lcp - ttfb );
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px"> } );
</span><span class="cx" style="display: block; padding: 0 10px"> } );
</span></span></pre></div>
<a id="trunktestsperformancespecshomeclassicthemetestjs"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/tests/performance/specs/home-classic-theme.test.js</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/tests/performance/specs/home-classic-theme.test.js 2023-08-16 00:13:45 UTC (rev 56398)
+++ trunk/tests/performance/specs/home-classic-theme.test.js 2023-08-16 08:46:22 UTC (rev 56399)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -4,7 +4,11 @@
</span><span class="cx" style="display: block; padding: 0 10px"> const { basename, join } = require( 'path' );
</span><span class="cx" style="display: block; padding: 0 10px"> const { writeFileSync } = require( 'fs' );
</span><span class="cx" style="display: block; padding: 0 10px"> const { exec } = require( 'child_process' );
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-const { getResultsFilename } = require( './../utils' );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+const {
+ getResultsFilename,
+ getTimeToFirstByte,
+ getLargestContentfulPaint,
+} = require( './../utils' );
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span><span class="cx" style="display: block; padding: 0 10px"> * WordPress dependencies.
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -16,15 +20,22 @@
</span><span class="cx" style="display: block; padding: 0 10px"> wpBeforeTemplate: [],
</span><span class="cx" style="display: block; padding: 0 10px"> wpTemplate: [],
</span><span class="cx" style="display: block; padding: 0 10px"> wpTotal: [],
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ timeToFirstByte: [],
+ largestContentfulPaint: [],
+ lcpMinusTtfb: [],
</ins><span class="cx" style="display: block; padding: 0 10px"> };
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> beforeAll( async () => {
</span><span class="cx" style="display: block; padding: 0 10px"> await activateTheme( 'twentytwentyone' );
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- await exec( 'npm run env:cli -- menu location assign all-pages primary' );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ await exec(
+ 'npm run env:cli -- menu location assign all-pages primary'
+ );
</ins><span class="cx" style="display: block; padding: 0 10px"> } );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> afterAll( async () => {
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- const resultsFilename = getResultsFilename( basename( __filename, '.js' ) );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ const resultsFilename = getResultsFilename(
+ basename( __filename, '.js' )
+ );
</ins><span class="cx" style="display: block; padding: 0 10px"> writeFileSync(
</span><span class="cx" style="display: block; padding: 0 10px"> join( __dirname, resultsFilename ),
</span><span class="cx" style="display: block; padding: 0 10px"> JSON.stringify( results, null, 2 )
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -42,14 +53,19 @@
</span><span class="cx" style="display: block; padding: 0 10px"> const [ navigationTiming ] = JSON.parse( navigationTimingJson );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> results.wpBeforeTemplate.push(
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- navigationTiming.serverTiming[0].duration
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ navigationTiming.serverTiming[ 0 ].duration
</ins><span class="cx" style="display: block; padding: 0 10px"> );
</span><span class="cx" style="display: block; padding: 0 10px"> results.wpTemplate.push(
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- navigationTiming.serverTiming[1].duration
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ navigationTiming.serverTiming[ 1 ].duration
</ins><span class="cx" style="display: block; padding: 0 10px"> );
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- results.wpTotal.push(
- navigationTiming.serverTiming[2].duration
- );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ results.wpTotal.push( navigationTiming.serverTiming[ 2 ].duration );
+
+ const ttfb = await getTimeToFirstByte();
+ const lcp = await getLargestContentfulPaint();
+
+ results.timeToFirstByte.push( ttfb );
+ results.largestContentfulPaint.push( lcp );
+ results.lcpMinusTtfb.push( lcp - ttfb );
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px"> } );
</span><span class="cx" style="display: block; padding: 0 10px"> } );
</span></span></pre></div>
<a id="trunktestsperformanceutilsjs"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/tests/performance/utils.js</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/tests/performance/utils.js 2023-08-16 00:13:45 UTC (rev 56398)
+++ trunk/tests/performance/utils.js 2023-08-16 08:46:22 UTC (rev 56399)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -21,13 +21,58 @@
</span><span class="cx" style="display: block; padding: 0 10px"> * @return {string} Result file name.
</span><span class="cx" style="display: block; padding: 0 10px"> */
</span><span class="cx" style="display: block; padding: 0 10px"> function getResultsFilename( fileName ) {
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- const prefixArg = process.argv.find( ( arg ) => arg.startsWith( '--prefix' ) );
- const fileNamePrefix = prefixArg ? `${prefixArg.split( '=' )[1]}-` : '';
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ const prefixArg = process.argv.find( ( arg ) =>
+ arg.startsWith( '--prefix' )
+ );
+ const fileNamePrefix = prefixArg ? `${ prefixArg.split( '=' )[ 1 ] }-` : '';
</ins><span class="cx" style="display: block; padding: 0 10px"> const resultsFilename = fileNamePrefix + fileName + '.results.json';
</span><span class="cx" style="display: block; padding: 0 10px"> return resultsFilename;
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+/**
+ * Returns time to first byte (TTFB) using the Navigation Timing API.
+ *
+ * @see https://web.dev/ttfb/#measure-ttfb-in-javascript
+ *
+ * @return {Promise<number>}
+ */
+async function getTimeToFirstByte() {
+ return page.evaluate( () => {
+ const { responseStart, startTime } =
+ performance.getEntriesByType( 'navigation' )[ 0 ];
+ return responseStart - startTime;
+ } );
+}
+
+/**
+ * Returns the Largest Contentful Paint (LCP) value using the dedicated API.
+ *
+ * @see https://w3c.github.io/largest-contentful-paint/
+ * @see https://web.dev/lcp/#measure-lcp-in-javascript
+ *
+ * @return {Promise<number>}
+ */
+async function getLargestContentfulPaint() {
+ return page.evaluate(
+ () =>
+ new Promise( ( resolve ) => {
+ new PerformanceObserver( ( entryList ) => {
+ const entries = entryList.getEntries();
+ // The last entry is the largest contentful paint.
+ const largestPaintEntry = entries.at( -1 );
+
+ resolve( largestPaintEntry?.startTime || 0 );
+ } ).observe( {
+ type: 'largest-contentful-paint',
+ buffered: true,
+ } );
+ } )
+ );
+}
+
</ins><span class="cx" style="display: block; padding: 0 10px"> module.exports = {
</span><span class="cx" style="display: block; padding: 0 10px"> median,
</span><span class="cx" style="display: block; padding: 0 10px"> getResultsFilename,
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ getTimeToFirstByte,
+ getLargestContentfulPaint,
</ins><span class="cx" style="display: block; padding: 0 10px"> };
</span></span></pre>
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