Marc Mintel
5397309103
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100 lines
4.0 KiB
Plaintext
100 lines
4.0 KiB
Plaintext
Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
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const types = require('../../types.js');
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const bindReporter = require('./lib/bindReporter.js');
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const getVisibilityWatcher = require('./lib/getVisibilityWatcher.js');
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const initMetric = require('./lib/initMetric.js');
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const initUnique = require('./lib/initUnique.js');
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const LayoutShiftManager = require('./lib/LayoutShiftManager.js');
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const observe = require('./lib/observe.js');
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const runOnce = require('./lib/runOnce.js');
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const onFCP = require('./onFCP.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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/** Thresholds for CLS. See https://web.dev/articles/cls#what_is_a_good_cls_score */
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const CLSThresholds = [0.1, 0.25];
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/**
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* Calculates the [CLS](https://web.dev/articles/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/articles/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 = (onReport, opts = {}) => {
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// Start monitoring FCP so we can only report CLS if FCP is also reported.
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// Note: this is done to match the current behavior of CrUX.
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onFCP.onFCP(
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runOnce.runOnce(() => {
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const metric = initMetric.initMetric('CLS', 0);
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let report;
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const visibilityWatcher = getVisibilityWatcher.getVisibilityWatcher();
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const layoutShiftManager = initUnique.initUnique(opts, LayoutShiftManager.LayoutShiftManager);
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const handleEntries = (entries) => {
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for (const entry of entries) {
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layoutShiftManager._processEntry(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 (layoutShiftManager._sessionValue > metric.value) {
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metric.value = layoutShiftManager._sessionValue;
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metric.entries = layoutShiftManager._sessionEntries;
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report();
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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, CLSThresholds, opts.reportAllChanges);
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visibilityWatcher.onHidden(() => {
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handleEntries(po.takeRecords() );
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report(true);
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});
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// Queue a task to report (if nothing else triggers a report first).
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// This allows CLS to be reported as soon as FCP fires when
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// `reportAllChanges` is true.
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types.WINDOW?.setTimeout?.(report);
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}
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}),
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);
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};
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exports.CLSThresholds = CLSThresholds;
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exports.onCLS = onCLS;
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//# sourceMappingURL=getCLS.js.map
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