web-vitals/src/lib/whenIdleOrHidden.ts

Easily measure performance metrics in JavaScript

/*
 * 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: () => void) => {
  // Cap the requestIdleCallback to 1 sec for very busy apps
  // https://github.com/GoogleChrome/web-vitals/issues/754
  // If not using rIC, then the setTimeout timeout should be 0
  const timeout = 'requestIdleCallback' in globalThis ? 1000 : 0;

  const rIC = globalThis.requestIdleCallback || setTimeout;
  const cIC = globalThis.cancelIdleCallback || clearTimeout;

  // 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 {
    const wrappedCb = runOnce(cb);

    let idleHandle = -1;
    const onHidden = () => {
      cIC(idleHandle);
      wrappedCb();
    };

    addEventListener('visibilitychange', onHidden, {once: true, capture: true});
    idleHandle = rIC(
      () => {
        removeEventListener('visibilitychange', onHidden, {capture: true});
        wrappedCb();
      },
      {timeout: timeout},
    );
  }
};