52 lines
1.7 KiB
JavaScript
52 lines
1.7 KiB
JavaScript
function waitForAnimationFrames(count) {
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return new Promise(resolve => {
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if (count-- <= 0) {
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resolve();
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} else {
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requestAnimationFrame(() => {
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waitForAnimationFrames(count).then(resolve);
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});
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}
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});
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}
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// Asserts that there is currently no FCP reported. Pass t to add some wait, in case CSS is loaded
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// and FCP is incorrectly fired afterwards.
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async function assertNoFirstContentfulPaint(t) {
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await waitForAnimationFrames(3);
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assert_equals(performance.getEntriesByName('first-contentful-paint').length, 0, 'First contentful paint marked too early. ');
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}
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// Function that is resolved once FCP is reported, using PerformanceObserver. It rejects after a long
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// wait time so that failing tests don't timeout.
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async function assertFirstContentfulPaint(t) {
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return new Promise(resolve => {
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function checkFCP() {
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if (performance.getEntriesByName('first-contentful-paint').length === 1) {
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resolve();
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} else {
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t.step_timeout(checkFCP, 0);
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}
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}
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t.step(checkFCP);
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});
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}
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async function test_fcp(label, before_assert_fcp_func) {
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setup({"hide_test_state": true});
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const style = document.createElement('style');
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document.head.appendChild(style);
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await promise_test(async t => {
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assert_implements(window.PerformancePaintTiming, "Paint Timing isn't supported.");
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const main = document.getElementById('main');
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await new Promise(r => window.addEventListener('load', r));
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await assertNoFirstContentfulPaint(t);
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main.className = 'preFCP';
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await assertNoFirstContentfulPaint(t);
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if (before_assert_fcp_func) {
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await before_assert_fcp_func();
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}
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main.className = 'contentful';
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await assertFirstContentfulPaint(t);
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}, label);
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}
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