web-vitals
Version:
Easily measure performance metrics in JavaScript
59 lines • 2.57 kB
JavaScript
/*
* 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.
*/
/**
* Takes a performance entry type and a callback function, and creates a
* `PerformanceObserver` instance that will observe the specified entry type
* with buffering enabled and call the callback _for each entry_.
*
* This function also feature-detects entry support and wraps the logic in a
* try/catch to avoid errors in unsupporting browsers.
*/
export const observe = (types, callback, opts = {}) => {
try {
const supportedTypes = types.filter((t) => PerformanceObserver.supportedEntryTypes.includes(t));
if (supportedTypes.length > 0) {
const po = new PerformanceObserver((list) => {
// Delay by a microtask to workaround a bug in Safari where the
// callback is invoked immediately, rather than in a separate task.
// See: https://github.com/GoogleChrome/web-vitals/issues/277
queueMicrotask(() => {
const entries = list.getEntries();
// When observing more than one entry type, entries from different
// types can be delivered out of order, so sort by end time
// (startTime + duration) to ensure they're in the right order.
// See: https://github.com/w3c/performance-timeline/issues/224
if (supportedTypes.length > 1) {
entries.sort((a, b) => {
const scoreA = a.startTime + a.duration;
const scoreB = b.startTime + b.duration;
return scoreA - scoreB;
});
}
callback(entries);
});
});
for (const t of supportedTypes) {
po.observe({ type: t, buffered: true, ...opts });
}
return po;
}
}
catch {
// Do nothing.
}
return;
};
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