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/*
* 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.
*/
import {bindReporter} from './lib/bindReporter.js';
import {initMetric} from './lib/initMetric.js';
import {onBFCacheRestore} from './lib/bfcache.js';
import {getNavigationEntry} from './lib/getNavigationEntry.js';
import {MetricRatingThresholds, ReportOpts, TTFBMetric} from './types.js';
import {getActivationStart} from './lib/getActivationStart.js';
import {whenActivated} from './lib/whenActivated.js';
/** Thresholds for TTFB. See https://web.dev/articles/ttfb#what_is_a_good_ttfb_score */
export const TTFBThresholds: MetricRatingThresholds = [800, 1800];
/**
* Runs in the next task after the page is done loading and/or prerendering.
* @param callback
*/
const whenReady = (callback: () => void) => {
if (document.prerendering) {
whenActivated(() => whenReady(callback));
} else if (document.readyState !== 'complete') {
addEventListener('load', () => whenReady(callback), true);
} else {
// Queue a task so the callback runs after `loadEventEnd`.
setTimeout(callback, 0);
}
};
/**
* 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: (metric: TTFBMetric) => void,
opts?: ReportOpts,
) => {
// Set defaults
opts = opts || {};
let metric = initMetric('TTFB');
let report = bindReporter(
onReport,
metric,
TTFBThresholds,
opts.reportAllChanges,
);
whenReady(() => {
const navigationEntry = getNavigationEntry();
if (navigationEntry) {
// The activationStart reference is used because TTFB should be
// relative to page activation rather than navigation start if the
// page was prerendered. But in cases where `activationStart` occurs
// after the first byte is received, this time should be clamped at 0.
metric.value = Math.max(
navigationEntry.responseStart - getActivationStart(),
0,
);
metric.entries = [navigationEntry];
report(true);
// Only report TTFB after bfcache restores if a `navigation` entry
// was reported for the initial load.
onBFCacheRestore(() => {
metric = initMetric('TTFB', 0);
report = bindReporter(
onReport,
metric,
TTFBThresholds,
opts!.reportAllChanges,
);
report(true);
});
}
});
};
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