metric-helpers.ts•3.47 kB
/**
* Common metric calculation helpers
*/
import type { LighthouseReport } from '../../types/index.js';
export interface CoreWebVitals {
lcp: number;
fcp: number;
cls: number;
tbt: number;
ttfb?: number;
fid?: number;
inp?: number;
}
/**
* Extract Core Web Vitals from a Lighthouse report
*/
export function extractCoreWebVitals(report: LighthouseReport): CoreWebVitals {
const audits = report.audits;
return {
lcp: audits['largest-contentful-paint']?.numericValue || 0,
fcp: audits['first-contentful-paint']?.numericValue || 0,
cls: audits['cumulative-layout-shift']?.numericValue || 0,
tbt: audits['total-blocking-time']?.numericValue || 0,
ttfb: audits['time-to-first-byte']?.numericValue,
fid: audits['max-potential-fid']?.numericValue,
inp: audits['interaction-to-next-paint']?.numericValue,
};
}
/**
* Get audit weight from category configuration
*/
export function getAuditWeight(
report: LighthouseReport,
auditId: string,
categoryId: string = 'performance'
): number {
const category = report.categories?.[categoryId as keyof typeof report.categories];
if (!category) return 0;
const auditRef = category.auditRefs?.find((ref: any) => ref.id === auditId);
return auditRef?.weight || 0;
}
/**
* Calculate weighted score impact
*/
export function calculateWeightedImpact(score: number, weight: number): number {
return (1 - score) * weight;
}
/**
* Get performance score from report
*/
export function getPerformanceScore(report: LighthouseReport): number {
return report.categories?.performance?.score || 0;
}
/**
* Extract opportunities from report
*/
export interface Opportunity {
id: string;
title: string;
score: number;
savingsBytes?: number;
savingsMs?: number;
}
export function extractOpportunities(report: LighthouseReport): Opportunity[] {
const opportunities: Opportunity[] = [];
for (const [id, audit] of Object.entries(report.audits)) {
if (audit && audit.details?.type === 'opportunity' && audit.score !== null && audit.score < 1) {
opportunities.push({
id,
title: audit!.title,
score: audit!.score,
savingsBytes: (audit!.details as any).overallSavingsBytes,
savingsMs: (audit!.details as any).overallSavingsMs,
});
}
}
return opportunities;
}
/**
* Calculate total savings from opportunities
*/
export function calculateTotalSavings(opportunities: Opportunity[]): {
bytes: number;
ms: number;
} {
return opportunities.reduce((acc, opp) => {
acc.bytes += opp.savingsBytes || 0;
acc.ms += opp.savingsMs || 0;
return acc;
}, { bytes: 0, ms: 0 });
}
/**
* Check if metric passes threshold
*/
export function checkMetricThreshold(
value: number,
thresholds: { good: number; poor: number },
lowerIsBetter: boolean = true
): 'good' | 'needs-improvement' | 'poor' {
if (lowerIsBetter) {
if (value <= thresholds.good) return 'good';
if (value <= thresholds.poor) return 'needs-improvement';
return 'poor';
} else {
if (value >= thresholds.good) return 'good';
if (value >= thresholds.poor) return 'needs-improvement';
return 'poor';
}
}
/**
* Standard thresholds for Core Web Vitals
*/
export const CWV_THRESHOLDS = {
lcp: { good: 2500, poor: 4000 },
fcp: { good: 1800, poor: 3000 },
cls: { good: 0.1, poor: 0.25 },
tbt: { good: 200, poor: 600 },
ttfb: { good: 800, poor: 1800 },
inp: { good: 200, poor: 500 },
};