In-Memory Transport

A transport that stores logs in memory for testing and debugging. Provides an API to retrieve emitted logs programmatically.

Overview

The in-memory transport is designed specifically for testing and debugging scenarios. It stores all logs in an array that can be retrieved and inspected programmatically.

import { createInMemoryLoggerTransport } from '@crowlog/logger';

const inMemoryTransport = createInMemoryLoggerTransport();

Basic Usage

Simple Example

import { createInMemoryLoggerTransport, createLogger } from '@crowlog/logger';

const inMemoryTransport = createInMemoryLoggerTransport();

const logger = createLogger({
  namespace: 'my-app',
  transports: [inMemoryTransport]
});

logger.info('First log');
logger.error({ userId: '123' }, 'Second log');

// Retrieve logs
const logs = inMemoryTransport.getLogs();
console.log(logs);
// [
//   {
//     level: 'info',
//     message: 'First log',
//     timestampMs: 1738878633123,
//     namespace: 'my-app',
//     data: {}
//   },
//   {
//     level: 'error',
//     message: 'Second log',
//     timestampMs: 1738878633456,
//     namespace: 'my-app',
//     data: { userId: '123' }
//   }
// ]

API

getLogs(options?)

Retrieve all stored logs.

type GetLogsOptions = {
  excludeTimestampMs?: boolean;
};

function getLogs(options?: GetLogsOptions): LoggerTransportLogArgs[];

Parameters

Parameter	Type	Default	Description
excludeTimestampMs	boolean	false	Omit timestampMs from results

Returns

Array of log objects containing:

{
  level: 'debug' | 'info' | 'warn' | 'error';
  message: string;
  timestampMs: number; // Omitted if excludeTimestampMs: true
  namespace: string;
  data: Record<string, unknown>;
}

Testing with In-Memory Transport

Unit Tests

Perfect for asserting log output in unit tests:

import { createInMemoryLoggerTransport, createLogger } from '@crowlog/logger';
import { describe, expect, test } from 'vitest';

describe('User service', () => {
  test('logs user creation', async () => {
    const inMemoryTransport = createInMemoryLoggerTransport();

    const logger = createLogger({
      namespace: 'user-service',
      transports: [inMemoryTransport]
    });

    await createUser({ logger, name: 'Alice' });

    const logs = inMemoryTransport.getLogs({ excludeTimestampMs: true });

    expect(logs).toEqual([
      {
        level: 'info',
        message: 'User created',
        namespace: 'user-service',
        data: { name: 'Alice' }
      }
    ]);
  });
});

Deterministic Tests

Use excludeTimestampMs: true for deterministic assertions:

test('logs payment processing', () => {
  const inMemoryTransport = createInMemoryLoggerTransport();
  const logger = createLogger({
    namespace: 'payment',
    transports: [inMemoryTransport]
  });

  processPayment({ logger, amount: 100 });

  // Timestamps are excluded for predictable snapshots
  const logs = inMemoryTransport.getLogs({ excludeTimestampMs: true });

  expect(logs).toMatchSnapshot();
});

Limitations

Memory Growth

In-memory transport stores logs indefinitely. For long-running tests or large test suites, this can cause memory issues.

Solution: Clear logs between tests or use a fresh transport for each test.

No Automatic Cleanup

Unlike stdout which automatically flushes, in-memory logs persist until explicitly cleared or garbage collected.

Solution: Create new transports in beforeEach hooks.

Production Use

Never use in production! Use stdout transport or custom transports for production logging.

See Also

• Stdout Transport - Default production transport
• Custom Transports - Create your own transports
• Testing Guide - Testing patterns with Crowlog