getCLS.js
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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 { initMetric } from './lib/initMetric.js';
import { observe } from './lib/observe.js';
import { onHidden } from './lib/onHidden.js';
import { bindReporter } from './lib/bindReporter.js';
export const getCLS = (onReport, reportAllChanges = false) => {
const metric = initMetric('CLS', 0);
let report;
const entryHandler = (entry) => {
// Only count layout shifts without recent user input.
if (!entry.hadRecentInput) {
metric.value += entry.value;
metric.entries.push(entry);
report();
}
};
const po = observe('layout-shift', entryHandler);
if (po) {
report = bindReporter(onReport, metric, po, reportAllChanges);
onHidden(({ isUnloading }) => {
po.takeRecords().map(entryHandler);
if (isUnloading) {
metric.isFinal = true;
}
report();
});
}
};