web-vitals/dist/modules/types/fcp.d.ts

Easily measure performance metrics in JavaScript

import { LoadState, Metric, ReportCallback } from './base.js';
import { NavigationTimingPolyfillEntry } from './polyfills.js';
/**
 * An FCP-specific version of the Metric object.
 */
export interface FCPMetric extends Metric {
    name: 'FCP';
    entries: PerformancePaintTiming[];
}
/**
 * An object containing potentially-helpful debugging information that
 * can be sent along with the FCP value for the current page visit in order
 * to help identify issues happening to real-users in the field.
 */
export interface FCPAttribution {
    /**
     * The time from when the user initiates loading the page until when the
     * browser receives the first byte of the response (a.k.a. TTFB).
     */
    timeToFirstByte: number;
    /**
     * The delta between TTFB and the first contentful paint (FCP).
     */
    firstByteToFCP: number;
    /**
     * The loading state of the document at the time when FCP `occurred (see
     * `LoadState` for details). Ideally, documents can paint before they finish
     * loading (e.g. the `loading` or `dom-interactive` phases).
     */
    loadState: LoadState;
    /**
     * The `PerformancePaintTiming` entry corresponding to FCP.
     */
    fcpEntry?: PerformancePaintTiming;
    /**
     * The `navigation` entry of the current page, which is useful for diagnosing
     * general page load issues.
     */
    navigationEntry?: PerformanceNavigationTiming | NavigationTimingPolyfillEntry;
}
/**
 * An FCP-specific version of the Metric object with attribution.
 */
export interface FCPMetricWithAttribution extends FCPMetric {
    attribution: FCPAttribution;
}
/**
 * An FCP-specific version of the ReportCallback function.
 */
export interface FCPReportCallback extends ReportCallback {
    (metric: FCPMetric): void;
}
/**
 * An FCP-specific version of the ReportCallback function with attribution.
 */
export interface FCPReportCallbackWithAttribution extends FCPReportCallback {
    (metric: FCPMetricWithAttribution): void;
}