web-vitals
Version:
Easily measure performance metrics in JavaScript
46 lines (45 loc) • 1.69 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.
*/
const getRating = (value, thresholds) => {
if (value > thresholds[1]) {
return 'poor';
}
if (value > thresholds[0]) {
return 'needs-improvement';
}
return 'good';
};
export const bindReporter = (callback, metric, thresholds, reportAllChanges) => {
let prevValue;
let delta;
return (forceReport) => {
if (metric.value >= 0) {
if (forceReport || reportAllChanges) {
delta = metric.value - (prevValue || 0);
// Report the metric if there's a non-zero delta or if no previous
// value exists (which can happen in the case of the document becoming
// hidden when the metric value is 0).
// See: https://github.com/GoogleChrome/web-vitals/issues/14
if (delta || prevValue === undefined) {
prevValue = metric.value;
metric.delta = delta;
metric.rating = getRating(metric.value, thresholds);
callback(metric);
}
}
}
};
};