@quern/react-native-os-logger

Send React Native JS logs to Apple's Unified Logging System (os_log) and Android's Log, with subsystem/category support for easy filtering in Console.app, log CLI, and Quern.

Why?

React Native's default console.log output goes to stdout/stderr and gets mixed in with everything else. By routing logs through os_log (iOS) and android.util.Log (Android), you get:

• Subsystem & category filtering — find your app's logs instantly in Console.app or with log stream --predicate
• Log levels — debug, info, default, error, fault — with appropriate system behavior (persistence, throttling)
• Quern integration — logs appear in Quern's log viewer, filterable by your app's subsystem
• Native tooling — works with Instruments, log collect, and any tool that reads the unified log

Installation

npm install @quern/react-native-os-logger
# or
yarn add @quern/react-native-os-logger

iOS

cd ios && pod install

Android

No additional setup needed.

Usage

Drop-in console.log replacement

import { patchConsole } from '@quern/react-native-os-logger';

// Call once at app startup — that's it
patchConsole('com.myapp');

// All console methods now route through os_log
console.log('This appears in Console.app');    // → OS_LOG_TYPE_DEFAULT
console.info('Info message');                   // → OS_LOG_TYPE_INFO
console.debug('Debug message');                 // → OS_LOG_TYPE_DEBUG
console.warn('Warning!');                       // → OS_LOG_TYPE_ERROR
console.error('Something broke');               // → OS_LOG_TYPE_ERROR

Original console methods are preserved — logs still appear in Metro as usual.

Explicit API

import { configure, logInfo, logError } from '@quern/react-native-os-logger';

// Call once at app startup
configure('com.myapp', 'js');

logInfo('App started');
logError('Something went wrong');

Multiple loggers with different categories

Each createLogger call creates a separate os_log_t (iOS) or Log tag (Android), so you can filter by category independently:

import { createLogger } from '@quern/react-native-os-logger';

const netLogger = createLogger('com.myapp', 'networking');
const uiLogger = createLogger('com.myapp', 'ui');

netLogger.info('GET /api/users → 200 OK');
netLogger.error('POST /api/login → 401');

uiLogger.debug('ProfileScreen rendered in 12ms');
uiLogger.info('User tapped "Save" button');

Filter in Console.app:

# Just networking logs
log stream --predicate 'subsystem == "com.myapp" AND category == "networking"'

Log levels

JS Method	iOS (os_log)	Android (Log)	Notes
logDebug	OS_LOG_TYPE_DEBUG	Log.d	Not persisted by default on iOS
logInfo	OS_LOG_TYPE_INFO	Log.i	Not persisted by default on iOS
logDefault	OS_LOG_TYPE_DEFAULT	Log.i	Persisted on iOS
logError	OS_LOG_TYPE_ERROR	Log.e	Persisted, captures caller info
logFault	OS_LOG_TYPE_FAULT	Log.wtf	Persisted, captures stack

Filtering in Console.app / log CLI

# Stream logs from your app's subsystem
log stream --predicate 'subsystem == "com.myapp"'

# Filter by category
log stream --predicate 'subsystem == "com.myapp" AND category == "networking"'

API

configure(subsystem: string, category: string): void

Configure the logger with a reverse-DNS subsystem identifier and a category. Call once at startup.

logDefault(message: string): void

logInfo(message: string): void

logDebug(message: string): void

logError(message: string): void

logFault(message: string): void

log(level: LogLevel, message: string): void

createLogger(subsystem: string, category: string): Logger

Creates a new logger with its own os_log_t (iOS) / Log tag (Android). Returns an object with default, info, debug, error, fault, and log methods. Multiple loggers can coexist with different categories.

patchConsole(subsystem: string, category?: string): void

Patches console.log/info/debug/warn/error to route through os_log. Original methods are preserved. Category defaults to "console". Call once at startup.

Requirements

• React Native 0.76+ (New Architecture / TurboModules)
• iOS 13+
• Android API 21+

License

MIT