/* * Copyright 2020 Google LLC * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import { bindReporter } from './lib/bindReporter.js'; import { getVisibilityWatcher } from './lib/getVisibilityWatcher.js'; import { initMetric } from './lib/initMetric.js'; import { observe } from './lib/observe.js'; import { onBFCacheRestore } from './lib/onBFCacheRestore.js'; import { onHidden } from './lib/onHidden.js'; const reportedMetricIDs = {}; export const getLCP = (onReport, reportAllChanges) => { const visibilityWatcher = getVisibilityWatcher(); let metric = initMetric('LCP'); let report; const entryHandler = (entry) => { // The startTime attribute returns the value of the renderTime if it is not 0, // and the value of the loadTime otherwise. const value = entry.startTime; // If the page was hidden prior to paint time of the entry, // ignore it and mark the metric as final, otherwise add the entry. if (value < visibilityWatcher.firstHiddenTime) { metric.value = value; metric.entries.push(entry); report(); } }; const po = observe('largest-contentful-paint', entryHandler); if (po) { report = bindReporter(onReport, metric, reportAllChanges); const stopListening = () => { if (!reportedMetricIDs[metric.id]) { po.takeRecords().map(entryHandler); po.disconnect(); reportedMetricIDs[metric.id] = true; report(true); } }; // Stop listening after input. Note: while scrolling is an input that // stop LCP observation, it's unreliable since it can be programmatically // generated. See: https://github.com/GoogleChrome/web-vitals/issues/75 ['keydown', 'click'].forEach((type) => { addEventListener(type, stopListening, { once: true, capture: true }); }); onHidden(stopListening, true); onBFCacheRestore((event) => { metric = initMetric('LCP'); report = bindReporter(onReport, metric, reportAllChanges); requestAnimationFrame(() => { requestAnimationFrame(() => { metric.value = performance.now() - event.timeStamp; reportedMetricIDs[metric.id] = true; report(true); }); }); }); } };