Frontend observability

Frontend Observability (the field side)

When to Use

Use this skill when you need a portable, framework-agnostic field-side observability system for any React or React Native app. Establishes one typed event taxonomy (canonical event-name constants, never inline strings), a best-effort non-blocking provider fan-out so a failing or absent analytics provider can never...

Portable skill — readable by Claude Code, OpenCode, Codex, Cursor, Windsurf, and others. This skill describes a field-side observability system — event taxonomy, provider fan-out, real-user vitals, error reporting, consent — not a dashboard or a specific vendor. It is the field complement to the frontend-lighthouse skill: Lighthouse is the lab gate (synthetic, pre-merge); this is the field (what real users actually experience). It lives in a services/analytics/ module per the frontend-architecture skill.

The goal: you can answer "what are real users doing, and what are they experiencing?" — with a typed event vocabulary (no stringly-typed track("clicked_thing") scattered everywhere), a fan-out that is best-effort (a broken provider never breaks the app), real Core Web Vitals from the field, and consent respected before anything fires.

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0. The five core ideas

1. Events are a typed vocabulary. Event names are canonical constants with a union type — never inline string literals. The taxonomy is reviewable in one file and the compiler rejects typos.
2. Fan-out is best-effort and non-blocking. track() dispatches to every provider, each in its own try/catch. A missing global, a thrown provider, an unloaded script — none can throw into the caller or stop the other providers.
3. One entry point, SSR-safe. A single track(event, props) is the only way to record. It's reached through a context hook that no-ops outside a provider and on the server, so instrumented components render safely anywhere.
4. Field vitals complement lab budgets. Real-user LCP/INP/CLS are reported to the same fan-out. Lighthouse proves the build can be fast; field vitals prove it is — together they close the loop.
5. Consent gates everything. No telemetry (events, vitals, error reports with PII) fires before opt-in. Consent state is checked at the fan-out boundary, not sprinkled through call sites.

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1. Directory layout

The system is one service module plus its constants (per frontend-architecture).

src/
├── constants/
│   └── analytics.ts           ← canonical event names + AnalyticsEvent union
├── services/analytics/
│   ├── index.ts               ← barrel: track, adapters, types
│   ├── track.ts               ← the best-effort fan-out (single entry point)
│   ├── adapters.ts            ← one (event, props) => void per provider, window-guarded
│   ├── web-vitals.ts          ← report real-user LCP/INP/CLS into track()
│   └── consent.ts             ← consent gate read by the fan-out
├── providers/
│   └── AnalyticsProvider.tsx  ← 'use client' context exposing useAnalytics().track
└── error/
    └── ErrorBoundary.tsx      ← reports caught render errors via the fan-out

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2. The event taxonomy (typed, never inline)

One file owns every event name. Components reference constants; the union type makes typos a compile error and the catalog a single source of truth.

// constants/analytics.ts
export const ANALYTICS_EVENTS = {
  PROJECT_CLICK: "project_click",
  GITHUB_CLICK: "github_click",
  RESUME_DOWNLOAD: "resume_download",
  CONTACT_SUBMISSION: "contact_submission",
} as const;

export type AnalyticsEvent =
  (typeof ANALYTICS_EVENTS)[keyof typeof ANALYTICS_EVENTS];

// CORRECT — typed constant, autocompletes, can't typo
track(ANALYTICS_EVENTS.GITHUB_CLICK, { url });

// WRONG — stringly-typed, drifts, no compile check
track("github-click"); // ❌ silently a different event from "github_click"

Hard rules:

• No inline event-name strings anywhere; only ANALYTICS_EVENTS.*.
• Event names are snake_case and stable — renaming one breaks historical dashboards, so treat the catalog as a contract.
• Keep props shapes small and PII-light (see §6); prefer ids over names, never raw emails.

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3. Best-effort, non-blocking fan-out

track() is the single entry point. It iterates the adapter registry, guarding each call so one provider can't affect the caller or the others.

// services/analytics/track.ts
import type { AnalyticsEvent } from "@/constants/analytics";
import { analyticsAdapters } from "./adapters";
import { hasConsent } from "./consent";

export function track(
  event: AnalyticsEvent,
  props?: Record<string, unknown>,
): void {
  if (!hasConsent()) return; // §6 — nothing fires before opt-in
  for (const adapter of analyticsAdapters) {
    try {
      adapter(event, props);
    } catch {
      /* best-effort: a failing/absent provider must never throw into the
         caller or block dispatch to the remaining provider