61 lines
2.2 KiB
JavaScript
61 lines
2.2 KiB
JavaScript
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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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import { onBFCacheRestore } from './onBFCacheRestore.js';
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import { onHidden } from './onHidden.js';
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let firstHiddenTime = -1;
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const initHiddenTime = () => {
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return document.visibilityState === 'hidden' ? 0 : Infinity;
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};
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const trackChanges = () => {
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// Update the time if/when the document becomes hidden.
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onHidden(({ timeStamp }) => {
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firstHiddenTime = timeStamp;
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}, true);
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};
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export const getVisibilityWatcher = () => {
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if (firstHiddenTime < 0) {
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// If the document is hidden when this code runs, assume it was hidden
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// since navigation start. This isn't a perfect heuristic, but it's the
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// best we can do until an API is available to support querying past
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// visibilityState.
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if (window.__WEB_VITALS_POLYFILL__) {
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firstHiddenTime = window.webVitals.firstHiddenTime;
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if (firstHiddenTime === Infinity) {
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trackChanges();
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}
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}
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else {
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firstHiddenTime = initHiddenTime();
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trackChanges();
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}
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// Reset the time on bfcache restores.
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onBFCacheRestore(() => {
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// Schedule a task in order to track the `visibilityState` once it's
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// had an opportunity to change to visible in all browsers.
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// https://bugs.chromium.org/p/chromium/issues/detail?id=1133363
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setTimeout(() => {
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firstHiddenTime = initHiddenTime();
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trackChanges();
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}, 0);
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});
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}
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return {
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get firstHiddenTime() {
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return firstHiddenTime;
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}
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};
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};
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