Frequently Asked Questions (FAQ)

Common questions and answers about @nextrush/log.

Installation & Setup

How do I install @nextrush/log?

npm install @nextrush/log
# or
pnpm add @nextrush/log
# or
yarn add @nextrush/log
# or
bun add @nextrush/log

Does it work with TypeScript?

Yes! Full TypeScript support with complete type definitions included. No additional @types package needed.

What runtimes are supported?

Runtime	Supported	Notes
Node.js	✅	v16+ recommended
Bun	✅	Full support
Deno	✅	Use npm: specifier
Browser	✅	Works in all modern browsers
React	✅	Dedicated hooks and providers
Next.js	✅	Client and server components
Edge (Cloudflare/Vercel)	✅	Zero Node.js dependencies

How do I use it in Deno?

import { createLogger } from 'npm:@nextrush/log';

const log = createLogger('MyApp');
log.info('Works in Deno!');

---

Global Configuration

How do I disable ALL logging with one line?

import { disableLogging } from '@nextrush/log';

disableLogging(); // Done! All loggers are silent.

If I have 400+ files using createLogger, do I need to change them all?

No! Global configuration is a singleton - configure once, affects all files:

// src/lib/logger.ts - Configure ONCE
import { configure } from '@nextrush/log';

configure({ enabled: false }); // Affects ALL 400+ files!

All other files just use createLogger() normally - they automatically respect global config.

Where should I call configure() or disableLogging()?

At your app's entry point, before other code runs:

App Type	Where to Configure
Node.js	src/index.ts or src/main.ts
React/Vite	src/main.tsx (before <App />)
Next.js	_app.tsx or root layout.tsx
Express	Before app.listen()

What if multiple files import configure?

Importing doesn't call the function. Only the file that calls configure() changes settings. It's safe to import everywhere.

How do I reset configuration to defaults?

import { resetGlobalConfig } from '@nextrush/log';

resetGlobalConfig(); // Back to factory defaults

---

Log Levels

What are the available log levels?

Level	Priority	Use Case
trace	10	Detailed debugging (function entry/exit)
debug	20	Development debugging
info	30	Normal operations (default in production)
warn	40	Potential issues
error	50	Recoverable errors
fatal	60	Critical failures

How does level filtering work?

Setting minLevel logs that level and all higher priority levels:

const log = createLogger('App', { minLevel: 'warn' });

log.debug('ignored'); // ❌ Priority 20 < 40
log.info('ignored');  // ❌ Priority 30 < 40
log.warn('logged');   // ✅ Priority 40 = 40
log.error('logged');  // ✅ Priority 50 > 40
log.fatal('logged');  // ✅ Priority 60 > 40

How do I change log level at runtime?

const log = createLogger('App');

// Change level dynamically
log.setLevel('error'); // Now only error + fatal

// Check before expensive operations
if (log.isLevelEnabled('debug')) {
  log.debug('Data', computeExpensiveData());
}

Why are my debug logs not showing in production?

By default, production (NODE_ENV=production) uses minLevel: 'info'. Debug and trace are filtered out.

To enable debug logs in production:

const log = createLogger('App', {
  env: 'production',
  minLevel: 'debug', // Override the default
});

---

Environment & Production

How does environment detection work?

The logger reads NODE_ENV automatically:

NODE_ENV	minLevel	Output	Redaction
development	trace	Pretty	Off
test	trace	Pretty	Off
production	info	JSON	On

Why are my debug logs showing in Vite production build?

Vite uses import.meta.env.MODE instead of NODE_ENV. Force production mode:

const log = createLogger('App', {
  env: 'production' // Force production mode
});

// Or configure globally
configure({ env: 'production' });

How do I get JSON output?

Set pretty: false or use env: 'production':

const log = createLogger('App', { pretty: false });
// OR
const log = createLogger('App', { env: 'production' });

How do I get colorful output in production?

const log = createLogger('App', {
  env: 'production',
  pretty: true,  // Override JSON output
  colors: true,  // Enable colors
});

---

Sensitive Data

What fields are automatically redacted?

By default in production, these fields are redacted:

• password, passwd, pwd
• token, accessToken, refreshToken
• secret, apiKey, apiSecret
• authorization, auth
• cookie, session
• creditCard, cardNumber, cvv
• ssn, socialSecurity

How do I add custom sensitive fields?

const log = createLogger('App', {
  sensitiveKeys: ['customSecret', 'myApiKey', 'internalToken'],
});

How do I disable redaction?

const log = createLogger('App', { redact: false });

WARNING

Never disable redaction in production - sensitive data will be logged!

Does redaction work in nested objects?

Yes! Redaction is recursive:

log.info('Data', {
  user: {
    name: 'John',
    auth: {
      password: 'secret123', // → "[REDACTED]"
    },
  },
});

---

Child Loggers

What is a child logger?

A child logger inherits parent settings and adds a namespace prefix:

const log = createLogger('App');
const db = log.child('Database');
const api = log.child('API');

db.info('Connected');  // [App:Database] Connected
api.info('Ready');     // [App:API] Ready

Do child loggers respect global config?

Yes! Child loggers inherit global configuration just like parent loggers.

Can I create deeply nested children?

Yes:

const log = createLogger('App');
const api = log.child('API');
const users = api.child('Users');
const create = users.child('Create');

create.info('User created'); // [App:API:Users:Create] User created

---

Performance

Is logging expensive?

Logging is designed to be cheap:

• Level checks are fast (number comparison)
• Disabled logs are no-ops (almost zero cost)
• Serialization only happens for enabled logs

How do I avoid expensive computations for disabled logs?

// ❌ Bad: Always computes even if debug is disabled
log.debug('Data', { result: expensiveComputation() });

// ✅ Good: Only compute if level is enabled
if (log.isLevelEnabled('debug')) {
  log.debug('Data', { result: expensiveComputation() });
}

How do I measure performance?

const timer = log.time('db-query');
const result = await db.query('SELECT * FROM users');
timer.end('Query done', { rows: result.length });
// Output: "Query done" { duration: 42, rows: 150 }

---

Transports

What is a transport?

A transport is a function that receives log entries and does something with them (e.g., send to a server, write to file).

const myTransport = (entry) => {
  fetch('/api/logs', {
    method: 'POST',
    body: JSON.stringify(entry),
  });
};

const log = createLogger('App');
log.addTransport(myTransport);

What is a global transport?

A global transport receives logs from ALL loggers in your app:

import { addGlobalTransport } from '@nextrush/log';

addGlobalTransport((entry) => {
  if (entry.level === 'error') {
    sendToSentry(entry);
  }
});

How do I batch logs before sending?

Use createBatchTransport:

import { createBatchTransport } from '@nextrush/log';

const { transport, flush } = createBatchTransport(
  async (logs) => {
    await fetch('/api/logs', {
      method: 'POST',
      body: JSON.stringify(logs),
    });
  },
  { batchSize: 50, flushInterval: 5000 }
);

const log = createLogger('App');
log.addTransport(transport);

// Flush before shutdown
process.on('SIGTERM', async () => {
  await flush();
  process.exit(0);
});

---

React & Browser

How do I use in React?

import { LoggerProvider, useLogger } from '@nextrush/log/react';

function App() {
  return (
    <LoggerProvider context="MyApp" options={{ minLevel: 'debug' }}>
      <MyComponent />
    </LoggerProvider>
  );
}

function MyComponent() {
  const log = useLogger('MyComponent');
  return <button onClick={() => log.info('Clicked!')}>Click</button>;
}

How do I disable logging in React production builds?

<LoggerProvider
  context="MyApp"
  globalConfig={{
    enabled: process.env.NODE_ENV !== 'production',
  }}
>
  {children}
</LoggerProvider>

Does it work with Next.js App Router?

Yes! Works in both client and server components:

// Server Component
import { createLogger } from '@nextrush/log';
const log = createLogger('ServerComponent');

// Client Component
'use client';
import { useLogger } from '@nextrush/log/react';

How do I see logs in browser DevTools?

Logs automatically go to browser console. Use DevTools → Console tab.

---

Namespace Filtering

How do I log only from specific modules?

import { enableNamespaces, createLogger } from '@nextrush/log';

// Only log from api and auth
enableNamespaces(['api:*', 'auth:*']);

createLogger('api:users').info('Logged');    // ✅
createLogger('db:queries').info('Ignored');  // ❌

What patterns are supported?

Pattern	Matches
*	Everything
api:*	api:users, api:auth, api:orders:create
auth:login	Only auth:login (exact)

How do I disable specific namespaces?

import { enableNamespaces, disableNamespaces } from '@nextrush/log';

enableNamespaces(['*']);           // Enable everything
disableNamespaces(['verbose:*']);  // Except verbose

---

Troubleshooting

My logs are not appearing

1. Check if logging is enabled:

   import { getGlobalConfig } from '@nextrush/log';
   console.log(getGlobalConfig()); // Check enabled, minLevel

2. Check log level:

   const log = createLogger('App');
   console.log(log.isLevelEnabled('debug')); // false if level too high

3. Check namespace filtering:

   import { isNamespaceEnabled } from '@nextrush/log';
   console.log(isNamespaceEnabled('your:namespace'));

My logs are showing "[REDACTED]"

Redaction is on (usually in production). Either:

• Check you're not logging sensitive fields unintentionally
• Disable redaction for development: { redact: false }

TypeError: createLogger is not a function

Check your import:

// ✅ Correct
import { createLogger } from '@nextrush/log';

// ❌ Wrong
import createLogger from '@nextrush/log';

React: useLogger must be used within LoggerProvider

Wrap your app with LoggerProvider:

function App() {
  return (
    <LoggerProvider context="App">
      {/* Your components here */}
    </LoggerProvider>
  );
}

Logs are appearing twice

You might have added the same transport twice, or have both console transport and pretty: true. Check your transports:

const log = createLogger('App');
console.log(log); // Inspect transports array

---

Architecture & Design

Why singleton pattern instead of DI?

Logging is a cross-cutting concern used everywhere in an application. The singleton pattern:

1. Simplicity - No need to pass logger through every function
2. Industry standard - Winston, Pino, Bunyan all use singletons
3. Testability - resetGlobalConfig() makes tests isolated
4. Performance - No DI container overhead

Is it tree-shakeable?

Yes! Import only what you need:

// Only imports createLogger, not global config functions
import { createLogger } from '@nextrush/log';

Does it have any dependencies?

Zero dependencies. The entire library is self-contained.

Is it safe to use in serverless/edge?

Yes! Designed for:

• Cloudflare Workers
• Vercel Edge Functions
• AWS Lambda@Edge
• Deno Deploy

No file system or Node.js-specific APIs required.

---

Migration

Migrating from console.log

// Before
console.log('User created:', userId);

// After
import { createLogger } from '@nextrush/log';
const log = createLogger('App');
log.info('User created', { userId });

Migrating from Winston

// Winston
const winston = require('winston');
const logger = winston.createLogger({ level: 'info' });
logger.info('Hello', { user: 'john' });

// @nextrush/log
import { createLogger } from '@nextrush/log';
const log = createLogger('App', { minLevel: 'info' });
log.info('Hello', { user: 'john' });

Migrating from Pino

// Pino
const pino = require('pino');
const logger = pino({ level: 'info' });
logger.info({ user: 'john' }, 'Hello');

// @nextrush/log (data comes last)
import { createLogger } from '@nextrush/log';
const log = createLogger('App', { minLevel: 'info' });
log.info('Hello', { user: 'john' });

---

See Also

• Getting Started
• Global Configuration
• Best Practices
• API Reference
• Examples