| 1 | /*
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| 2 | * Copyright 2020 Google LLC
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| 3 | *
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| 4 | * Licensed under the Apache License, Version 2.0 (the "License");
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| 5 | * you may not use this file except in compliance with the License.
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| 6 | * You may obtain a copy of the License at
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| 7 | *
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| 8 | * https://www.apache.org/licenses/LICENSE-2.0
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| 9 | *
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| 10 | * Unless required by applicable law or agreed to in writing, software
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| 11 | * distributed under the License is distributed on an "AS IS" BASIS,
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| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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| 13 | * See the License for the specific language governing permissions and
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| 14 | * limitations under the License.
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| 15 | */
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| 16 |
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| 17 | let firstHiddenTime =
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| 18 | document.visibilityState === 'hidden' ? 0 : Infinity;
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| 19 |
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| 20 | const onVisibilityChange = (event: Event) => {
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| 21 | if (document.visibilityState === 'hidden') {
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| 22 | firstHiddenTime = event.timeStamp;
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| 23 | removeEventListener('visibilitychange', onVisibilityChange, true);
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| 24 | }
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| 25 | }
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| 26 |
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| 27 | // Note: do not add event listeners unconditionally (outside of polyfills).
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| 28 | addEventListener('visibilitychange', onVisibilityChange, true);
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| 29 |
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| 30 | export const getFirstHiddenTime = () => firstHiddenTime;
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