sickn33/agentic-awesome-skills/frontend-observability

Frontend Observability (the field side)

When to Use

Use this skill when you need a portable, framework-agnostic field-side observability pattern for React or React Native integrations. Defines a typed taxonomy and best-effort provider dispatch with explicit consent, privacy and runtime limitations.

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 (provider exceptions are isolated where supported), real Core Web Vitals from the field, and consent respected before anything fires.

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, not a scheduling guarantee. track() dispatches to every provider, each with synchronous and asynchronous error handling. A missing global, a thrown provider, an unloaded script — ordinary caught exceptions/rejections do not propagate; synchronous vendor work can still block the thread.
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 samples controlled conditions; field vitals estimate actual experiences for the observed population — 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.

Runtime and privacy contract

These are independent integration sketches, not complete compiled modules. Supply the missing globals, config, imports, Props and error classifier; pin vendor APIs. Try/catch cannot prevent synchronous CPU blocking, infinite loops or SDK background effects. Adapters must do bounded work, return their promises, avoid raw logging and share per-provider rate/queue limits. Use actual keyboard/SSR/unmount/rejection tests.

Allowlist property names, types and sizes before dispatch; TypeScript types do not validate runtime input. IDs can identify people; URLs may contain tokens or query PII. Send a route/category label rather than a raw href, error message or stack. Treat cross-vendor fan-out as separate data disclosures requiring the approved purposes and destinations.

A boolean track gate does not stop SDK auto-collection, cookies, session replay or queued sends. Configure collection disabled before native SDK startup, delay scripts/init until permitted, disable and clear provider state/queues on withdrawal, and recheck consent after every awaited initialization. A dynamic import may still execute module effects; choose SDK loading that satisfies actual requirements. Consent storage failures default to denied. Do not hydrate a module-global consent state from user requests on SSR. React Server Components cannot call this client hook; conventional SSR only uses the no-op outside the provider. Native vitals are not web Core Web Vitals, and React Native Firebase requires a compatible native build rather than arbitrary Expo Go.

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

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",
  WEB_VITAL: "web_vital",
  CLIENT_ERROR: "client_error",
} 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.

3. Best-effort fan-out with bounded adapter work

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 {
      void Promise.resolve(adapter(event, props)).catch(() => {
        // Drop provider failures; never recurse into analytics or log raw data.
      });
    } catch {
      /* best-effort: a failing/absent provider must never throw into the
         caller or block dispatch to the remaining providers. */
    }
  }
}

Each adapter is a tiny (event, props) => void that guards its provider global — it no-ops on the server (no window) and when the provider script is absent, so a missing or unloaded provider never throws.

// services/analytics/adapters.ts
import type { AnalyticsEvent } from "@/constants/analytics";
// Supply AnalyticsGlobals type declarations and a platform-specific firebaseAdapter import.
export type AnalyticsAdapter = (
  event: AnalyticsEvent,
  props?: Record<string, unknown>,
) => void | Promise<void>;
export const googleAnalyticsAdapter: AnalyticsAdapter = (event, props) => {
  const w =
    typeof window !== "undefined" ? (window as AnalyticsGlobals) : undefined;
  if (!w || typeof w.gtag !== "function") return; // SSR-safe + absent-safe
  w.gtag("event", event, props ?? {});
};
export const clarityAdapter: AnalyticsAdapter = (event) => {
  const w =
    typeof window !== "undefined" ? (window as AnalyticsGlobals) : undefined;
  if (!w || typeof w.clarity !== "function") return;
  w.clarity("event", event);
};
// The registry track() fans out across. Exported + mutable so tests can swap
// in a recording sink to assert dispatch.
export const analyticsAdapters: AnalyticsAdapter[] = [
  googleAnalyticsAdapter,
  clarityAdapter,
  firebaseAdapter,
  // posthogAdapter, openPanelAdapter, …
];

3.1 Firebase Analytics — one adapter, two platforms

Firebase Analytics ships two SDKs that share the same `logEvent(name, params)` contract, so a single conceptual adapter covers both web and React Native — only the import and the "is it available?" guard differ. On web the adapter never imports the SDK at module top level (it's browser-only and async), so it stays SSR-safe.

// services/analytics/adapters.firebase.web.ts — Firebase JS SDK (web)
import type { Analytics } from "firebase/analytics";
import { hasConsent } from "./consent";
import type { AnalyticsAdapter } from "./adapters";
// Held after a lazy, browser-only init (below) so the adapter stays synchronous + SSR-safe.
let analytics: Analytics | undefined;
export function setFirebaseAnalytics(instance: Analytics): void {
  analytics = instance;
}
export const firebaseAdapter: AnalyticsAdapter = (event, props) => {
  if (typeof window === "undefined" || !analytics) return; // SSR-safe + not-yet-ready safe
  return import("firebase/analytics").then(({ logEvent }) => {
    if (!hasConsent() || !analytics) return; // recheck after async work
    logEvent(analytics, event, props);
  });
};

// services/analytics/firebase.init.ts — lazy, browser-only init (web)
import { initializeApp, getApps } from "firebase/app";
import { hasConsent } from "./consent";
import { setFirebaseAnalytics } from "./adapters.firebase.web";
import { FIREBASE_CONFIG } from "@/constants/analytics";
export async function initFirebaseAnalytics(): Promise<void> {
  if (typeof window === "undefined") return; // never on the server
  if (!hasConsent()) return;
  const { getAnalytics, isSupported } = await import("firebase/analytics");
  if (!(await isSupported()) || !hasConsent()) return; // unsupported browser → no-op
  const app = getApps()[0] ?? initializeApp(FIREBASE_CONFIG);
  setFirebaseAnalytics(getAnalytics(app)); // adapter goes live after this
}

// services/analytics/adapters.firebase.native.ts — @react-native-firebase/analytics (RN / Expo)
import analytics from "@react-native-firebase/analytics";
import type { AnalyticsAdapter } from "./adapters";
export const firebaseAdapter: AnalyticsAdapter = (event, props) => {
  // RN: no window; the native module is present once the app boots.
  return analytics().logEvent(event, props);
};

Same shape, two files. Resolve the platform variant by file extension (adapters.firebase.native.ts via Metro's .native.ts resolution, or a Platform.OS switch) so the registry, `track` fan-out, consent gate, taxonomy, and `useAnalytics` hook never change across platforms. Verify Firebase event-name/parameter restrictions and reserved names for the pinned SDK. Snake_case is this taxonomy convention, not the full provider validation contract. Gate initFirebaseAnalytics() on consent (§6) — Firebase also exposes setAnalyticsCollectionEnabled(false) to harden the opt-out.

Why this shape: analytics is the _last_ thing that should crash an app. A vendor script that fails to load, a global that isn't there yet, an adapter that throws on a malformed prop — all are contained. The registry being exported and mutable makes dispatch unit-testable without mounting any provider.

4. The provider + hook (SSR-safe entry)

A 'use client' context exposes track through useAnalytics(). Outside a provider (tests, server) it returns a no-op, so instrumented components never throw in isolation.

// providers/AnalyticsProvider.tsx
"use client";
import { createContext, useContext, useMemo, type ReactNode } from "react";
import { track as trackEvent } from "@/services/analytics";
import type { AnalyticsEvent } from "@/constants/analytics";