You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 

64 lines
2.4 KiB

/*
* 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 { initMetric } from './lib/initMetric.js';
const afterLoad = (callback) => {
if (document.readyState === 'complete') {
// Queue a task so the callback runs after `loadEventEnd`.
setTimeout(callback, 0);
}
else {
// Queue a task so the callback runs after `loadEventEnd`.
addEventListener('load', () => setTimeout(callback, 0));
}
};
const getNavigationEntryFromPerformanceTiming = () => {
// Really annoying that TypeScript errors when using `PerformanceTiming`.
const timing = performance.timing;
const navigationEntry = {
entryType: 'navigation',
startTime: 0,
};
for (const key in timing) {
if (key !== 'navigationStart' && key !== 'toJSON') {
navigationEntry[key] = Math.max(timing[key] -
timing.navigationStart, 0);
}
}
return navigationEntry;
};
export const getTTFB = (onReport) => {
const metric = initMetric('TTFB');
afterLoad(() => {
try {
// Use the NavigationTiming L2 entry if available.
const navigationEntry = performance.getEntriesByType('navigation')[0] ||
getNavigationEntryFromPerformanceTiming();
metric.value = metric.delta =
navigationEntry.responseStart;
// In some cases the value reported is negative or is larger
// than the current page time. Ignore these cases:
// https://github.com/GoogleChrome/web-vitals/issues/137
// https://github.com/GoogleChrome/web-vitals/issues/162
if (metric.value < 0 || metric.value > performance.now())
return;
metric.entries = [navigationEntry];
onReport(metric);
}
catch (error) {
// Do nothing.
}
});
};