111 lines
3.9 KiB
JavaScript
111 lines
3.9 KiB
JavaScript
Object.defineProperty(exports, '__esModule', { value: true });
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const bindReporter = require('./lib/bindReporter.js');
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const initMetric = require('./lib/initMetric.js');
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const observe = require('./lib/observe.js');
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const onHidden = require('./lib/onHidden.js');
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/*
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* Copyright 2020 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/**
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* Calculates the [CLS](https://web.dev/cls/) value for the current page and
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* calls the `callback` function once the value is ready to be reported, along
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* with all `layout-shift` performance entries that were used in the metric
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* value calculation. The reported value is a `double` (corresponding to a
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* [layout shift score](https://web.dev/cls/#layout-shift-score)).
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*
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* If the `reportAllChanges` configuration option is set to `true`, the
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* `callback` function will be called as soon as the value is initially
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* determined as well as any time the value changes throughout the page
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* lifespan.
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*
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* _**Important:** CLS should be continually monitored for changes throughout
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* the entire lifespan of a page—including if the user returns to the page after
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* it's been hidden/backgrounded. However, since browsers often [will not fire
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* additional callbacks once the user has backgrounded a
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* page](https://developer.chrome.com/blog/page-lifecycle-api/#advice-hidden),
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* `callback` is always called when the page's visibility state changes to
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* hidden. As a result, the `callback` function might be called multiple times
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* during the same page load._
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*/
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const onCLS = (
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onReport,
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options = {},
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) => {
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const metric = initMetric.initMetric('CLS', 0);
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let report;
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let sessionValue = 0;
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let sessionEntries = [];
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// const handleEntries = (entries: Metric['entries']) => {
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const handleEntries = (entries) => {
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entries.forEach(entry => {
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// Only count layout shifts without recent user input.
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if (!entry.hadRecentInput) {
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const firstSessionEntry = sessionEntries[0];
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const lastSessionEntry = sessionEntries[sessionEntries.length - 1];
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// If the entry occurred less than 1 second after the previous entry and
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// less than 5 seconds after the first entry in the session, include the
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// entry in the current session. Otherwise, start a new session.
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if (
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sessionValue &&
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sessionEntries.length !== 0 &&
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entry.startTime - lastSessionEntry.startTime < 1000 &&
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entry.startTime - firstSessionEntry.startTime < 5000
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) {
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sessionValue += entry.value;
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sessionEntries.push(entry);
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} else {
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sessionValue = entry.value;
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sessionEntries = [entry];
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}
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// If the current session value is larger than the current CLS value,
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// update CLS and the entries contributing to it.
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if (sessionValue > metric.value) {
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metric.value = sessionValue;
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metric.entries = sessionEntries;
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if (report) {
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report();
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}
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}
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}
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});
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};
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const po = observe.observe('layout-shift', handleEntries);
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if (po) {
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report = bindReporter.bindReporter(onReport, metric, options.reportAllChanges);
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const stopListening = () => {
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handleEntries(po.takeRecords() );
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report(true);
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};
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onHidden.onHidden(stopListening);
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return stopListening;
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}
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return;
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};
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exports.onCLS = onCLS;
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//# sourceMappingURL=getCLS.js.map
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