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@effectstream/log

Package: @effectstream/log · Source

OpenTelemetry-instrumented structured logging for EffectStream. Wraps tslog and the OpenTelemetry SDK behind a single log object that emits both pretty console output (log.local) and OTLP traces/logs to your collector (log.remote).

Install​

bun add @effectstream/log
# or
npm install @effectstream/log

Standalone usage​

Any Node service that wants colored terminal logs plus OTLP export with one dependency.

import {
  ComponentNames,
  defaultOtelSetup,
  log,
  SeverityNumber,
} from "@effectstream/log";

// Initialize OpenTelemetry once at startup (optional — defaults work too).
defaultOtelSetup({ serviceName: "my-app" });

// Local-only: pretty console output, no OTLP.
log.local(
  "my-app",                  // component name (any string)
  "startup",                 // namespace
  SeverityNumber.INFO,
  (l) => l("started on port", 3000),
);

// Remote: console + OpenTelemetry log record + trace correlation.
log.remote(
  "my-app",
  "auth",
  SeverityNumber.INFO,
  (l) => l("user logged in", { userId: "u_123" }),
);

The deferred (l) => l(...) form means message construction is skipped entirely when the level is filtered out — handy when log arguments are expensive to format (JSON.stringify of a big object).

Point the SDK at any OTLP-compatible collector (Grafana Alloy, Tempo, Honeycomb, …) via the standard OTEL_EXPORTER_OTLP_ENDPOINT env var.

Inside EffectStream​

Every package in the framework — sync, runtime, batcher, sm — logs through this module so the whole node emits one consistent trace tree. The ComponentNames constants tag log records by component, which is what powers the orchestrator's per-component log views.

Key exports​

  • log.local(component, namespace, level, deferred) — console-only logging. level is SeverityNumber; deferred = (l) => l(...args) is called only if the level passes the filter.
  • log.localForce(...) — bypasses level filtering.
  • log.remote(...) — console + OpenTelemetry log record. Same signature as local.
  • log.remoteForce(...) — remote without level filtering.
  • log.formatMessage(...) — the formatter used internally; useful for custom transports.
  • defaultOtelSetup(opts) — one-call OpenTelemetry SDK setup with sensible defaults.
  • attachTransport(transport) — register a custom tslog transport (e.g. ship logs to a file).
  • SeverityNumber — re-export of OpenTelemetry severity levels.
  • ComponentNames — string-enum constants used to tag logs by component.
  • Namespace — string | string[] for log namespacing.

Examples​

Runnable: test/examples.test.ts.