65 lines
2.4 KiB
JavaScript
65 lines
2.4 KiB
JavaScript
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/*
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* Copyright 2020 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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import { initMetric } from './lib/initMetric.js';
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const afterLoad = (callback) => {
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if (document.readyState === 'complete') {
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// Queue a task so the callback runs after `loadEventEnd`.
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setTimeout(callback, 0);
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}
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else {
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// Queue a task so the callback runs after `loadEventEnd`.
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addEventListener('load', () => setTimeout(callback, 0));
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}
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};
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const getNavigationEntryFromPerformanceTiming = () => {
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// Really annoying that TypeScript errors when using `PerformanceTiming`.
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const timing = performance.timing;
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const navigationEntry = {
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entryType: 'navigation',
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startTime: 0,
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};
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for (const key in timing) {
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if (key !== 'navigationStart' && key !== 'toJSON') {
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navigationEntry[key] = Math.max(timing[key] -
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timing.navigationStart, 0);
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}
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}
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return navigationEntry;
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};
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export const getTTFB = (onReport) => {
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const metric = initMetric('TTFB');
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afterLoad(() => {
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try {
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// Use the NavigationTiming L2 entry if available.
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const navigationEntry = performance.getEntriesByType('navigation')[0] ||
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getNavigationEntryFromPerformanceTiming();
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metric.value = metric.delta =
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navigationEntry.responseStart;
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// In some cases the value reported is negative or is larger
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// than the current page time. Ignore these cases:
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// https://github.com/GoogleChrome/web-vitals/issues/137
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// https://github.com/GoogleChrome/web-vitals/issues/162
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if (metric.value < 0 || metric.value > performance.now())
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return;
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metric.entries = [navigationEntry];
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onReport(metric);
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}
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catch (error) {
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// Do nothing.
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}
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});
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};
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