AsyncContext

Async context propagation and structured logging for Node.js, with first-class framework integrations.

AsyncContext helps you carry contextual data across asynchronous boundaries without passing parameters through every function. It provides a Context wrapper around AsyncLocalStorage, ready-made middleware for popular frameworks, and a structured logger that automatically includes the active context in every log entry.

Highlights

• Consistent per-request context without parameter threading.
• Simple, direct API for reading and writing context anywhere in the async flow.
• Observability-ready with correlation IDs, tenant/user data, and tracing metadata.
• Full-featured logger with levels, redaction, sampling, timers, and transports.
• DX-friendly configuration via presets and environment variables.
• Zero runtime dependencies and performance-focused design.

Installation

npm i @marceloraineri/async-context

Quick start

import crypto from "node:crypto";
import { Context } from "@marceloraineri/async-context";

await Context.run({ requestId: crypto.randomUUID() }, async () => {
  Context.addValue("user", { id: 42, name: "Ada" });
  Context.addOptions({ feature: "beta", retry: 2 });

  await Promise.resolve();

  const store = Context.getStore();
  console.log(store?.requestId); // 184fa9a3-f967-4a98-9d8f-57152e7cbe64
  console.log(store?.user); // { id: 42, name: "Ada" }
  console.log(store?.options); // { feature: "beta", retry: 2 }
});

Structured logging

The logger automatically merges the active async context and supports redaction, sampling, timers, and JSON or pretty output.

import crypto from "node:crypto";
import { Context, createLogger } from "@marceloraineri/async-context";

const logger = createLogger({
  name: "api",
  level: "info",
  contextKey: "ctx",
  redactKeys: ["ctx.token", "data.password"],
});

await Context.run({ requestId: crypto.randomUUID(), token: "secret" }, async () => {
  logger.info("request started", { route: "/ping" });
});

By default, common sensitive keys (for example password, token, authorization) are automatically redacted. You can disable this with redactDefaults: false or add extra key names with redactFieldNames.

Timers and child loggers

import { createLogger } from "@marceloraineri/async-context";

const logger = createLogger({ name: "jobs", level: "debug" });
const jobLogger = logger.child({ job: "import-users" });

const end = jobLogger.startTimer("debug");
await Promise.resolve();
end("job completed");

const noisyLogger = logger.child({ job: "debug-import" }, { level: "trace" });
noisyLogger.trace("verbose logging enabled");

JSON output or custom transports

import { createConsoleTransport, createLogger } from "@marceloraineri/async-context";

const logger = createLogger({
  level: "info",
  transports: [createConsoleTransport({ format: "json" })],
});

logger.info("structured log", { feature: "json" });

OpenAI wrapper

Capture OpenAI call metadata inside the current async context.

import OpenAI from "openai";
import { Context, withOpenAIContext } from "@marceloraineri/async-context";

const openai = new OpenAI({ apiKey: process.env.OPENAI_API_KEY });

await Context.run({ requestId: "req_123" }, async () => {
  const response = await withOpenAIContext(
    "responses.create",
    { model: "gpt-4o", input: "Hello!" },
    (req) => openai.responses.create(req),
    { includeRequest: true }
  );

  console.log(response.id);
  console.log(Context.getValue("openai"));
});

By default, the wrapper appends summaries to the openai context key, and only includes safe request fields unless you explicitly allow more keys.

OpenTelemetry (optional)

Create spans, propagate trace context from headers, and sync baggage with AsyncContext when @opentelemetry/api is available.

import * as otel from "@opentelemetry/api";
import {
  Context,
  createAsyncContextExpressOpenTelemetryMiddleware,
  setOpenTelemetryBaggageFromContext,
  withOpenTelemetrySpan,
} from "@marceloraineri/async-context";

app.use(
  createAsyncContextExpressOpenTelemetryMiddleware({
    otel: {
      api: otel,
      tracerName: "api",
      contextAttributeKeys: ["requestId", "tenantId"],
    },
  })
);

await Context.run({ requestId: "req_1", tenantId: "t_123" }, async () => {
  await withOpenTelemetrySpan(
    "db.query",
    async () => Promise.resolve(),
    { api: otel, attributes: { db: "users" } }
  );

  setOpenTelemetryBaggageFromContext({
    api: otel,
    contextKeys: ["requestId", "tenantId"],
    baggagePrefix: "ctx.",
  });
});

Performance timing

Measure sync or async work and store timing data in the active context.

import { Context } from "@marceloraineri/async-context";

await Context.run({}, async () => {
  await Context.measure("db.query", async () => {
    await Promise.resolve();
  }, { data: { table: "users" } });

  console.log(Context.getValue("perf"));
});

Use key or mode to control where entries are stored.

Context.measure("cache.lookup", () => "hit", { key: "performance", mode: "overwrite" });

DX and configuration

Use presets or environment variables to configure logging without code changes.

import { createLoggerFromEnv, loggerPreset } from "@marceloraineri/async-context";

const logger = createLoggerFromEnv({
  name: "api",
  defaults: loggerPreset("production"),
  onWarning: (warning) => {
    console.warn(`[logger-env] ${warning.key}: ${warning.reason}`, {
      value: warning.value,
    });
  },
});

Environment variables:

Variable	Description	Example
LOG_PRESET	development, production, or test preset	production
LOG_LEVEL	Minimum log level (name or numeric)	info
LOG_FORMAT	json or pretty	json
LOG_COLORS	Enable ANSI colors	true
LOG_CONTEXT	Attach async context	true
LOG_CONTEXT_KEY	Key name for context	ctx
LOG_CONTEXT_KEYS	Comma-separated or JSON array allowlist	requestId,tenantId
LOG_REDACT_KEYS	Redaction paths (CSV or JSON array)	ctx.token,data.password
LOG_REDACT_DEFAULTS	Enable default sensitive-field redaction	true
LOG_REDACT_FIELDS	Extra sensitive field names (CSV or JSON array)	accessToken,creditCard
LOG_REDACT_PLACEHOLDER	Mask value placeholder	[REDACTED]
LOG_SAMPLE_RATE	0..1 or percent sampling	0.25
LOG_INCLUDE_PID	Include process id	true
LOG_INCLUDE_HOSTNAME	Include hostname	false
LOG_TIMESTAMP	Include timestamp	true
LOG_BINDINGS	JSON object or key=value pairs added to every log entry	{"service":"api","version":2}
LOG_NAME	Logger name	api

All LOG_ variables also accept LOGGER_ aliases (for example LOGGER_LEVEL). CSV list values accept commas or semicolons as separators. List env values are de-duplicated while preserving order.

Framework integrations

Express

AsyncContextExpresssMiddleware (with three "s") and AsyncContextExpressMiddleware (alias) create a new context per request and seed it with a unique instance_id.

import express from "express";
import { AsyncContextExpressMiddleware, Context } from "@marceloraineri/async-context";

const app = express();
app.use(AsyncContextExpressMiddleware);

app.get("/ping", (_req, res) => {
  const store = Context.getStore();
  res.json({ instanceId: store?.instance_id ?? null });
});

app.listen(3000, () => console.log("API listening on :3000"));

If you need a custom request id or seed data, use createAsyncContextExpressMiddleware.

import express from "express";
import { createAsyncContextExpressMiddleware, Context } from "@marceloraineri/async-context";

const app = express();

app.use(
  createAsyncContextExpressMiddleware({
    idKey: "request_id",
    seed: (req) => ({ method: req.method, path: req.url }),
  })
);

app.get("/ping", (_req, res) => {
  const store = Context.getStore();
  res.json({ requestId: store?.request_id ?? null });
});

Fastify

Use the onRequest hook or the convenience registration helper.

import fastify from "fastify";
import { createAsyncContextFastifyHook, Context } from "@marceloraineri/async-context";

const app = fastify();
app.addHook("onRequest", createAsyncContextFastifyHook());

app.get("/ping", async () => {
  const store = Context.getStore();
  return { instanceId: store?.instance_id ?? null };
});

Koa

import Koa from "koa";
import { createAsyncContextKoaMiddleware, Context } from "@marceloraineri/async-context";

const app = new Koa();
app.use(createAsyncContextKoaMiddleware());

app.use(async (ctx) => {
  const store = Context.getStore();
  ctx.body = { instanceId: store?.instance_id ?? null };
});

Next.js API routes

import type { NextApiRequest, NextApiResponse } from "next";
import { createAsyncContextNextHandler, Context } from "@marceloraineri/async-context";

export default createAsyncContextNextHandler(
  async (_req: NextApiRequest, res: NextApiResponse) => {
    const store = Context.getStore();
    res.status(200).json({ instanceId: store?.instance_id ?? null });
  }
);

NestJS

AsyncContextNestMiddleware reuses the Express integration to enable async context in Nest (Express adapter).

import { MiddlewareConsumer, Module, NestModule } from "@nestjs/common";
import { AsyncContextNestMiddleware } from "@marceloraineri/async-context";

@Module({})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(AsyncContextNestMiddleware).forRoutes("*");
  }
}

AdonisJS

AsyncContextAdonisMiddleware plugs into the AdonisJS pipeline and creates one context per request.

// app/Http/Middleware/AsyncContext.ts
import { AsyncContextAdonisMiddleware } from "@marceloraineri/async-context";

export default AsyncContextAdonisMiddleware;

Sentry (optional)

AsyncContext can enrich Sentry events with the active store. If @sentry/node is not installed, the helpers safely no-op. Sensitive fields are redacted by default. Disable with redactDefaults: false or add redactFieldNames.

import express from "express";
import {
  AsyncContextExpressMiddleware,
  initSentryWithAsyncContext,
  sentryAsyncContextExpressMiddleware,
  sentryErrorHandler,
} from "@marceloraineri/async-context";

initSentryWithAsyncContext({
  sentryInit: {
    dsn: process.env.SENTRY_DSN,
    tracesSampleRate: 1.0,
  },
  redactKeys: ["async_context.token"],
});

const app = express();
app.use(AsyncContextExpressMiddleware);
app.use(sentryAsyncContextExpressMiddleware());

app.get("/ping", (_req, res) => res.json({ ok: true }));

app.use(sentryErrorHandler());

API overview

• Context.run(store, callback) and Context.run(callback)
• Context.getStore() and Context.requireStore()
• Context.getValue(key) and Context.requireValue(key)
• Context.addValue(key, value) and Context.addObjectValue(values)
• Context.runWith(values, callback)
• Context.snapshot() and Context.reset()
• createLogger(options) and new Logger(options)
• Logger.child(bindings, options?), Logger.withBindings(bindings, callback, options?), and Logger.startTimer(level?)
• createConsoleTransport(options)
• createLoggerFromEnv(options) and loggerPreset(preset)
• parseBooleanEnv(value), parseNumberEnv(value), parseCsvEnv(value), parseLogLevelEnv(value), parseLogFormatEnv(value), parseLoggerPresetEnv(value)
• createAsyncContextExpressMiddleware(options)
• createAsyncContextFastifyHook(options) and registerAsyncContextFastify(app, options)
• createAsyncContextKoaMiddleware(options)
• createAsyncContextNextHandler(handler, options)
• withOpenTelemetrySpan(name, callback, options) and recordOpenTelemetrySpan(summary, options)
• createAsyncContextExpressOpenTelemetryMiddleware(options)
• createAsyncContextFastifyOpenTelemetryHook(options)
• createAsyncContextKoaOpenTelemetryMiddleware(options)
• createAsyncContextNextOpenTelemetryHandler(handler, options)
• setOpenTelemetryBaggageFromContext(options) and mergeContextFromOpenTelemetryBaggage(options)
• extractOpenTelemetryContextFromHeaders(headers, options) and injectOpenTelemetryContextToHeaders(headers, options)
• initSentryWithAsyncContext(options) and captureExceptionWithContext(error)

Best practices

• Avoid replacing the entire store object; prefer addValue and addObjectValue.
• Long-lived contexts can retain memory; always complete the flow (next() in middleware).
• AsyncLocalStorage is per-process, so each worker maintains its own context.

Contributing

Issues and pull requests are welcome. Include repro steps, tests, or concrete usage scenarios when possible.