@absolutejs/beacon

Tiny, zero-dependency browser SDK for the AbsoluteJS observability stack. ~2 KB gzipped.

Captures uncaught errors + unhandled rejections, records breadcrumbs (console / click / fetch / navigation), batches, and POSTs an envelope to @absolutejs/errors/ingest via navigator.sendBeacon / fetch keepalive.

Why it's not Effect-native (on purpose)

A browser SDK loads on every page for every user, so bytes are the dominant cost. Measured: an Effect-native client is ~108 KB gz; this is ~2 KB gz. The client has no trust boundary — it's a dumb producer of telemetry — so the Effect/Schema rigor lives server-side in @absolutejs/errors/ingest, which validates the untrusted POST body.

You lose nothing on type safety: the envelope is contract-locked to the ingest endpoint's accepted shape by a compile-time assertion (the type spans the wire; the runtime machinery does not). Change the shape on either side and the build breaks.

Install

bun add @absolutejs/beacon

Zero runtime dependencies.

Quick start

import { initBeacon, captureException } from "@absolutejs/beacon";

initBeacon({
  project: "web",
  endpoint: "https://api.example.com/ingest",
  release: import.meta.env.VITE_RELEASE,
  environment: "production",
});

// Uncaught errors + unhandled rejections are captured automatically.
// Manual capture anywhere:
try {
  await checkout();
} catch (e) {
  captureException(e, { tags: { component: "billing" } });
}

Or hold an instance instead of the global:

import { createBeacon } from "@absolutejs/beacon";
const beacon = createBeacon({ project: "web" });
beacon.setUser({ id: currentUserId });
beacon.captureMessage("checkout started", "info");

What it does

• Auto-capture — window.onerror + unhandledrejection (toggle via instrument).
• Breadcrumbs — console.error/warn, clicks, fetch (skipping its own ingest endpoint), and SPA navigations, in a ring buffer attached to each event.
• Batching — buffers up to maxBatch (default 30) / flushIntervalMs (default 5s); flushes reliably on pagehide / tab-hidden via sendBeacon.
• Context — setTags, setUser, per-call tags/extra, a per-session id.
• Sampling + redaction — sampleRate and a beforeSend(event) hook (return null to drop).
• Replay seam — getReplayId() stamps each event with the active session-replay id (wired by @absolutejs/replay).

API

createBeacon(options) => Beacon
initBeacon(options)   => Beacon   // also sets the global singleton
getBeacon()           => Beacon | undefined

// Beacon:
captureException(error, { level?, tags?, extra? })
captureMessage(message, level?)
addBreadcrumb({ message, type?, data? })
setTags(tags) · setUser(user | null)
flush() => Promise<void>          // buffered events out now
close() => Promise<void>          // remove listeners + final flush

// Global helpers (no-op until initBeacon): captureException, captureMessage, addBreadcrumb

SSR-safe: imported in a non-DOM environment, createBeacon returns a no-op.

License

BSL-1.1 with a named carveout against hosted error-tracking / session-replay SaaS (Sentry, Datadog, LogRocket). See LICENSE.