web-vitals/dist/modules/attribution/onTTFB.js

Easily measure performance metrics in JavaScript

/*
 * Copyright 2022 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 { onTTFB as unattributedOnTTFB } from '../onTTFB.js';
const attributeTTFB = (metric) => {
    // Use a default object if no other attribution has been set.
    let attribution = {
        waitingDuration: 0,
        cacheDuration: 0,
        dnsDuration: 0,
        connectionDuration: 0,
        requestDuration: 0,
    };
    if (metric.entries.length) {
        const navigationEntry = metric.entries[0];
        const activationStart = navigationEntry.activationStart || 0;
        // Measure from workerStart or fetchStart so any service worker startup
        // time is included in cacheDuration (which also includes other sw time
        // anyway, that cannot be accurately split out cross-browser).
        const waitEnd = Math.max((navigationEntry.workerStart || navigationEntry.fetchStart) -
            activationStart, 0);
        const dnsStart = Math.max(navigationEntry.domainLookupStart - activationStart, 0);
        const connectStart = Math.max(navigationEntry.connectStart - activationStart, 0);
        const connectEnd = Math.max(navigationEntry.connectEnd - activationStart, 0);
        attribution = {
            waitingDuration: waitEnd,
            cacheDuration: dnsStart - waitEnd,
            // dnsEnd usually equals connectStart but use connectStart over dnsEnd
            // for dnsDuration in case there ever is a gap.
            dnsDuration: connectStart - dnsStart,
            connectionDuration: connectEnd - connectStart,
            // There is often a gap between connectEnd and requestStart. Attribute
            // that to requestDuration so connectionDuration remains 0 for
            // service worker controlled requests were connectStart and connectEnd
            // are the same.
            requestDuration: metric.value - connectEnd,
            navigationEntry: navigationEntry,
        };
    }
    // Use Object.assign to set property to keep tsc happy.
    const metricWithAttribution = Object.assign(metric, { attribution });
    return metricWithAttribution;
};
/**
 * Calculates the [TTFB](https://web.dev/articles/ttfb) value for the
 * current page and calls the `callback` function once the page has loaded,
 * along with the relevant `navigation` performance entry used to determine the
 * value. The reported value is a `DOMHighResTimeStamp`.
 *
 * Note, this function waits until after the page is loaded to call `callback`
 * in order to ensure all properties of the `navigation` entry are populated.
 * This is useful if you want to report on other metrics exposed by the
 * [Navigation Timing API](https://w3c.github.io/navigation-timing/). For
 * example, the TTFB metric starts from the page's [time
 * origin](https://www.w3.org/TR/hr-time-2/#sec-time-origin), which means it
 * includes time spent on DNS lookup, connection negotiation, network latency,
 * and server processing time.
 */
export const onTTFB = (onReport, opts) => {
    unattributedOnTTFB((metric) => {
        const metricWithAttribution = attributeTTFB(metric);
        onReport(metricWithAttribution);
    }, opts);
};