You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
84 lines
3.2 KiB
84 lines
3.2 KiB
2 years ago
|
/*
|
||
|
|
* 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 { initMetric } from './lib/initMetric.js';
|
||
|
|
import { observe } from './lib/observe.js';
|
||
|
|
import { onHidden } from './lib/onHidden.js';
|
||
|
|
import { onBFCacheRestore } from './lib/onBFCacheRestore.js';
|
||
|
|
import { bindReporter } from './lib/bindReporter.js';
|
||
|
|
import { getFCP } from './getFCP.js';
|
||
|
|
let isMonitoringFCP = false;
|
||
|
|
let fcpValue = -1;
|
||
|
|
export const getCLS = (onReport, reportAllChanges) => {
|
||
|
|
// Start monitoring FCP so we can only report CLS if FCP is also reported.
|
||
|
|
// Note: this is done to match the current behavior of CrUX.
|
||
|
|
if (!isMonitoringFCP) {
|
||
|
|
getFCP((metric) => {
|
||
|
|
fcpValue = metric.value;
|
||
|
|
});
|
||
|
|
isMonitoringFCP = true;
|
||
|
|
}
|
||
|
|
const onReportWrapped = (arg) => {
|
||
|
|
if (fcpValue > -1) {
|
||
|
|
onReport(arg);
|
||
|
|
}
|
||
|
|
};
|
||
|
|
let metric = initMetric('CLS', 0);
|
||
|
|
let report;
|
||
|
|
let sessionValue = 0;
|
||
|
|
let sessionEntries = [];
|
||
|
|
const entryHandler = (entry) => {
|
||
|
|
// Only count layout shifts without recent user input.
|
||
|
|
if (!entry.hadRecentInput) {
|
||
|
|
const firstSessionEntry = sessionEntries[0];
|
||
|
|
const lastSessionEntry = sessionEntries[sessionEntries.length - 1];
|
||
|
|
// If the entry occurred less than 1 second after the previous entry and
|
||
|
|
// less than 5 seconds after the first entry in the session, include the
|
||
|
|
// entry in the current session. Otherwise, start a new session.
|
||
|
|
if (sessionValue &&
|
||
|
|
entry.startTime - lastSessionEntry.startTime < 1000 &&
|
||
|
|
entry.startTime - firstSessionEntry.startTime < 5000) {
|
||
|
|
sessionValue += entry.value;
|
||
|
|
sessionEntries.push(entry);
|
||
|
|
}
|
||
|
|
else {
|
||
|
|
sessionValue = entry.value;
|
||
|
|
sessionEntries = [entry];
|
||
|
|
}
|
||
|
|
// If the current session value is larger than the current CLS value,
|
||
|
|
// update CLS and the entries contributing to it.
|
||
|
|
if (sessionValue > metric.value) {
|
||
|
|
metric.value = sessionValue;
|
||
|
|
metric.entries = sessionEntries;
|
||
|
|
report();
|
||
|
|
}
|
||
|
|
}
|
||
|
|
};
|
||
|
|
const po = observe('layout-shift', entryHandler);
|
||
|
|
if (po) {
|
||
|
|
report = bindReporter(onReportWrapped, metric, reportAllChanges);
|
||
|
|
onHidden(() => {
|
||
|
|
po.takeRecords().map(entryHandler);
|
||
|
|
report(true);
|
||
|
|
});
|
||
|
|
onBFCacheRestore(() => {
|
||
|
|
sessionValue = 0;
|
||
|
|
fcpValue = -1;
|
||
|
|
metric = initMetric('CLS', 0);
|
||
|
|
report = bindReporter(onReportWrapped, metric, reportAllChanges);
|
||
|
|
});
|
||
|
|
}
|
||
|
|
};
|