getTTFB.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 {initMetric} from './lib/initMetric.js';
import {ReportHandler} from './types.js';
interface NavigationEntryShim {
// From `PerformanceNavigationTimingEntry`.
entryType: string;
startTime: number;
// From `performance.timing`.
connectEnd?: number;
connectStart?: number;
domComplete?: number;
domContentLoadedEventEnd?: number;
domContentLoadedEventStart?: number;
domInteractive?: number;
domainLookupEnd?: number;
domainLookupStart?: number;
fetchStart?: number;
loadEventEnd?: number;
loadEventStart?: number;
redirectEnd?: number;
redirectStart?: number;
requestStart?: number;
responseEnd?: number;
responseStart?: number;
secureConnectionStart?: number;
unloadEventEnd?: number;
unloadEventStart?: number;
}
type PerformanceTimingKeys =
'connectEnd' |
'connectStart' |
'domComplete' |
'domContentLoadedEventEnd' |
'domContentLoadedEventStart' |
'domInteractive' |
'domainLookupEnd' |
'domainLookupStart' |
'fetchStart' |
'loadEventEnd' |
'loadEventStart' |
'redirectEnd' |
'redirectStart' |
'requestStart' |
'responseEnd' |
'responseStart' |
'secureConnectionStart' |
'unloadEventEnd' |
'unloadEventStart';
const afterLoad = (callback: () => void) => {
if (document.readyState === 'complete') {
// Queue a task so the callback runs after `loadEventEnd`.
setTimeout(callback, 0);
} else {
// Use `pageshow` so the callback runs after `loadEventEnd`.
addEventListener('pageshow', callback);
}
}
const getNavigationEntryFromPerformanceTiming = () => {
// Really annoying that TypeScript errors when using `PerformanceTiming`.
const timing = performance.timing;
const navigationEntry: NavigationEntryShim = {
entryType: 'navigation',
startTime: 0,
};
for (const key in timing) {
if (key !== 'navigationStart' && key !== 'toJSON') {
navigationEntry[key as PerformanceTimingKeys] = Math.max(
timing[key as PerformanceTimingKeys] - timing.navigationStart, 0);
}
}
return navigationEntry as PerformanceNavigationTiming;
};
export const getTTFB = (onReport: ReportHandler) => {
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 as PerformanceNavigationTiming).responseStart;
metric.entries = [navigationEntry];
metric.isFinal = true;
onReport(metric);
} catch (error) {
// Do nothing.
}
});
};