web-vitals
Version:
Easily measure performance metrics in JavaScript
78 lines • 3.51 kB
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 { getBFCacheRestoreTime } from '../lib/bfcache.js';
import { getLoadState } from '../lib/getLoadState.js';
import { getNavigationEntry } from '../lib/getNavigationEntry.js';
import { initUnique } from '../lib/initUnique.js';
import { FCPEntryManager } from '../lib/FCPEntryManager.js';
import { checkSoftNavsEnabled } from '../lib/softNavs.js';
import { onFCP as unattributedOnFCP } from '../onFCP.js';
export const onFCP = (onReport, opts = {}) => {
opts = Object.assign({}, opts);
// Init the fcpEntryManager (which will already be initialised in the
// unattributed onFCP method if soft navigation reporting is enabled
// and so will return that fcpEntryManager, rather than a new one)
const fcpEntryManager = initUnique(opts, FCPEntryManager);
if (checkSoftNavsEnabled(opts)) {
fcpEntryManager._softNavigationEntryMap = new Map();
}
const attributeFCP = (metric) => {
// Use a default object if no other attribution has been set.
let attribution = {
timeToFirstByte: 0,
firstByteToFCP: metric.value,
loadState: getLoadState(getBFCacheRestoreTime()),
};
if (metric.navigationType !== 'soft-navigation') {
if (metric.entries.length) {
const navigationEntry = getNavigationEntry();
const fcpEntry = metric.entries.at(-1);
if (navigationEntry) {
const responseStart = navigationEntry.responseStart;
const activationStart = navigationEntry.activationStart || 0;
const ttfb = Math.max(0, responseStart - activationStart);
attribution = {
timeToFirstByte: ttfb,
firstByteToFCP: metric.value - ttfb,
loadState: getLoadState(metric.entries[0].startTime),
navigationEntry,
fcpEntry,
};
}
}
}
else {
// Lookup the soft navigation entry. Do not use getEntriesByType since
// that is limited to the first 50 navigation entries due to buffer size.
const navigationEntry = fcpEntryManager._softNavigationEntryMap?.get(metric.navigationId);
if (navigationEntry) {
attribution = {
timeToFirstByte: 0,
firstByteToFCP: metric.value,
loadState: 'complete',
navigationEntry,
};
}
}
// Use `Object.assign()` to ensure the original metric object is returned.
const metricWithAttribution = Object.assign(metric, { attribution });
return metricWithAttribution;
};
unattributedOnFCP((metric) => {
onReport(attributeFCP(metric));
}, opts);
};
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