getFirstHidden.ts
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/*
* Copyright 2020 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import {onHidden} from './onHidden.js';
let firstHiddenTime: number
export const getFirstHidden = () => {
if (firstHiddenTime === undefined) {
// If the document is hidden when this code runs, assume it was hidden
// since navigation start. This isn't a perfect heuristic, but it's the
// best we can do until an API is available to support querying past
// visibilityState.
firstHiddenTime = document.visibilityState === 'hidden' ? 0 : Infinity;
// Update the time if/when the document becomes hidden.
onHidden(({timeStamp}) => firstHiddenTime = timeStamp, true);
}
return {
get timeStamp() {
return firstHiddenTime;
}
}
};