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1/*
2 * Copyright 2020 Google LLC
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17import {onBFCacheRestore} from './onBFCacheRestore.js';
18import {onHidden} from './onHidden.js';
19
20let firstHiddenTime = -1;
21
22const initHiddenTime = () => {
23 return document.visibilityState === 'hidden' ? 0 : Infinity;
24}
25
26const trackChanges = () => {
27 // Update the time if/when the document becomes hidden.
28 onHidden(({timeStamp}) => {
29 firstHiddenTime = timeStamp
30 }, true);
31};
32
33export const getFirstHidden = () => {
34 if (firstHiddenTime < 0) {
35 // If the document is hidden when this code runs, assume it was hidden
36 // since navigation start. This isn't a perfect heuristic, but it's the
37 // best we can do until an API is available to support querying past
38 // visibilityState.
39 if (self.__WEB_VITALS_POLYFILL__) {
40 firstHiddenTime = self.webVitals.firstHiddenTime;
41 if (firstHiddenTime === Infinity) {
42 trackChanges();
43 }
44 } else {
45 firstHiddenTime = initHiddenTime();
46 trackChanges();
47 }
48
49 // Reset the time on bfcache restores.
50 onBFCacheRestore(() => {
51 // Schedule a task in order to track the `visibilityState` once it's
52 // had an opportunity to change to visible in all browsers.
53 // https://bugs.chromium.org/p/chromium/issues/detail?id=1133363
54 setTimeout(() => {
55 firstHiddenTime = initHiddenTime();
56 trackChanges();
57 }, 0);
58 });
59 }
60 return {
61 get timeStamp() {
62 return firstHiddenTime;
63 }
64 }
65};