web-vitals
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Easily measure performance metrics in JavaScript
47 lines (46 loc) • 1.89 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 { getLoadState } from '../lib/getLoadState.js';
import { getSelector } from '../lib/getSelector.js';
import { onFID as unattributedOnFID } from '../onFID.js';
const attributeFID = (metric) => {
const fidEntry = metric.entries[0];
const attribution = {
eventTarget: getSelector(fidEntry.target),
eventType: fidEntry.name,
eventTime: fidEntry.startTime,
eventEntry: fidEntry,
loadState: getLoadState(fidEntry.startTime),
};
// Use Object.assign to set property to keep tsc happy.
const metricWithAttribution = Object.assign(metric, { attribution });
return metricWithAttribution;
};
/**
* Calculates the [FID](https://web.dev/articles/fid) value for the current page and
* calls the `callback` function once the value is ready, along with the
* relevant `first-input` performance entry used to determine the value. The
* reported value is a `DOMHighResTimeStamp`.
*
* _**Important:** since FID is only reported after the user interacts with the
* page, it's possible that it will not be reported for some page loads._
*/
export const onFID = (onReport, opts) => {
unattributedOnFID((metric) => {
const metricWithAttribution = attributeFID(metric);
onReport(metricWithAttribution);
}, opts);
};