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/*
* 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);
});
});
});
}
};