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web-vitals

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Easily measure performance metrics in JavaScript

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/* * Copyright 2024 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 { runOnce } from './runOnce.js'; /** * Runs the passed callback during the next idle period, or immediately * if the browser's visibility state is (or becomes) hidden. */ export const whenIdleOrHidden = (cb) => { const rIC = globalThis.requestIdleCallback || setTimeout; // If the document is hidden, run the callback immediately, otherwise // race an idle callback with the next `visibilitychange` event. if (document.visibilityState === 'hidden') { cb(); } else { cb = runOnce(cb); document.addEventListener('visibilitychange', cb, { once: true }); rIC(() => { cb(); // Remove the above event listener since no longer required. // See: https://github.com/GoogleChrome/web-vitals/issues/622 document.removeEventListener('visibilitychange', cb); }); } };